Systems and methods for regulating output currents of power conversion systems

ABSTRACT

Systems and methods are provided for regulating a power conversion system. An example system controller includes: a signal generator configured to receive a converted signal and a first compensation signal and generate a second compensation signal based at least in part on the converted signal and the first compensation signal, the converted signal being associated with an input signal for a power conversion system; a modulation component configured to receive the second compensation signal and a ramping signal and generate a modulation signal based at least in part on the second compensation signal and the ramping signal; and a drive component configured to receive the modulation signal and output a drive signal based at least in part on the modulation signal to a switch to affect the first current, the drive signal being associated with an on-time period, the switch being closed during the on-time period.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201510413940.8, filed Jul. 15, 2015, incorporated by reference hereinfor all purposes. In addition, this application is acontinuation-in-part of U.S. patent application Ser. No. 14/272,323,filed May 7, 2014, claiming priority to Chinese Patent Application No.201410157557.6, filed Apr. 18, 2014, both of these applications beingincorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for currentregulation. Merely by way of example, the invention has been applied topower conversion systems in quasi-resonance mode. But it would berecognized that the invention has a much broader range of applicability.

Light emitting diodes (LEDs) are widely used for lighting applications.Oftentimes, approximately constant currents are used to control workingcurrents of LEDs to achieve constant brightness. FIG. 1 is a simplifieddiagram showing a conventional power conversation system for LEDlighting. The power conversion system 100 includes a controller 102,resistors 104, 124, 126 and 132, capacitors 106, 120 and 134, a diode108, a transformer 110 including a primary winding 112, a secondarywinding 114 and an auxiliary winding 116, a power switch 128, a currentsensing resistor 130, and a rectifying diode 118. The controller 102includes terminals (e.g., pins) 138, 140, 142, 144, 146 and 148. Forexample, the power switch 128 is a bipolar junction transistor. Inanother example, the power switch 128 is a MOS transistor.

An alternate-current (AC) input voltage 152 is applied to the system100. A bulk voltage 150 (e.g., a rectified voltage no smaller than 0 V)associated with the AC input voltage 152 is received by the resistor104. The capacitor 106 is charged in response to the bulk voltage 150,and a voltage 154 is provided to the controller 102 at the terminal 138(e.g., terminal VCC). If the voltage 154 is larger than a predeterminedthreshold voltage in magnitude, the controller 102 begins to operatenormally, and outputs a drive signal 156 through the terminal 142 (e.g.,terminal GATE). For example, the drive signal 156 is apulse-width-modulation (PWM) signal with a switching frequency and aduty cycle. The switch 128 is closed (e.g., being turned on) or open(e.g., being turned off) in response to the drive signal 156 so that theoutput current 158 is regulated to be approximately constant.

The auxiliary winding 116 charges the capacitor 106 through the diode108 when the switch 128 is opened (e.g., being turned off) in responseto the drive signal 156 so that the controller 102 can operate normally.For example, a feedback signal 160 is provided to the controller 102through the terminal 140 (e.g., terminal FB) in order to detect the endof a demagnetization process of the secondary winding 118 for chargingor discharging the capacitor 134 using an internal error amplifier inthe controller 102. In another example, the feedback signal 160 isprovided to the controller 102 through the terminal 140 (e.g., terminalFB) in order to detect the beginning and the end of the demagnetizationprocess of the secondary winding 118. The resistor 130 is used fordetecting a primary current 162 flowing through the primary winding 112,and a current-sensing signal 164 is provided to the controller 102through the terminal 144 (e.g., terminal CS) to be processed during eachswitching cycle. Peak magnitudes of the current-sensing signal 164 aresampled and provided to the internal error amplifier. The capacitor 120is used to maintain an output voltage 168 so as to keep a stable outputcurrent through an output load (e.g., one or more LEDs 122). Forexample, the system 100 operates in a quasi-resonant mode.

FIG. 2 is a simplified conventional diagram showing the controller 102as part of the system 100. The controller 102 includes a ramp-signalgenerator 202, an under-voltage lock-out (UVLO) component 204, amodulation component 206, a logic controller 208, a driving component210, a demagnetization detector 212, an error amplifier 216, and acurrent-sensing component 214.

As shown in FIG. 2, the UVLO component 204 detects the signal 154 andoutputs a signal 218. If the signal 154 is larger than a firstpredetermined threshold in magnitude, the controller 102 begins tooperate normally. If the signal 154 is smaller than a secondpredetermined threshold in magnitude, the controller 102 is turned offThe second predetermined threshold is smaller than the firstpredetermined threshold in magnitude. The error amplifier 216 receives asignal 220 from the current-sensing component 214 and a reference signal222 and outputs an amplified signal 224 to the modulation component 206.The modulation component 206 also receives a signal 228 from theramp-signal generator 202 and outputs a modulation signal 226. Forexample, the signal 228 is a ramping signal and increases, linearly ornon-linearly, to a peak magnitude during each switching period. Thelogic controller 208 processes the modulation signal 226 and outputs acontrol signal 230 to the driving component 210 which generates thesignal 156 to turn on or off the switch 128. For example, thedemagnetization detector 212 detects the feedback signal 160 and outputsa signal 232 for determining the end of the demagnetization process ofthe secondary winding 114. In another example, the demagnetizationdetector 212 detects the feedback signal 160 and outputs the signal 232for determining the beginning and the end of the demagnetization processof the secondary winding 114. In addition, the demagnetization detector212 outputs a trigger signal 298 to the logic controller 208 to start anext cycle. The controller 102 is configured to keep an on-time periodassociated with the modulation signal 226 approximately constant for agiven output load.

The controller 102 is operated in a voltage-mode where, for example, thesignal 224 from the error amplifier 216 and the signal 228 from theoscillator 202 are both voltage signals and are compared by thecomparator 206 to generate the modulation signal 226 to drive the powerswitch 128. Therefore, an on-time period associated with the powerswitch 128 is determined by the signal 224 and the signal 228.

FIG. 3 is a simplified conventional diagram showing the current-sensingcomponent 214 and the error amplifier 216 as parts of the controller102. The current-sensing component 214 includes a switch 302 and acapacitor 304. The error amplifier 216 includes switches 306 and 308, anoperational transconductance amplifier (OTA) 310.

As shown in FIG. 3, the current-sensing component 214 samples thecurrent-sensing signal 164 and the error amplifier 216 amplifies thedifference between the signal 220 and the reference signal 222.Specifically, the switch 302 is closed (e.g., being turned on) or open(e.g., being turned off) in response to a signal 314 in order to samplepeak magnitudes of the current-sensing signal 164 in different switchingperiods. If the switch 302 is closed (e.g., being turned on) in responseto the signal 314 and the switch 306 is open (e.g., being turned off) inresponse to the signal 232 from the demagnetization detector 212, thecapacitor 304 is charged and the signal 220 increases in magnitude. Ifthe switch 306 is closed (e.g., being turned on) in response to thesignal 232, the switch 308 is open (e.g., being turned off) in responseto a signal 312 and the difference between the signal 220 and thereference signal 222 is amplified by the amplifier 310. The signal 312and the signal 232 are complementary to each other. For example, duringthe demagnetization process of the secondary winding 114, the signal 232is at a logic high level. The switch 306 remains closed (e.g., beingturned on) and the switch 308 remains open (e.g., being turned off). TheOTA 310, together with the capacitor 134, performs integrationassociated with the signal 220.

Under stable normal operations, an average output current is determined,according to the following equation, without taking into account anyerror current:

$\begin{matrix}{\overset{\_}{I_{o}} = {\frac{1}{2} \times N \times \frac{V_{{ref}\_ {ea}}}{R_{cs}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where N represents a turns ratio between the primary winding 112 and thesecondary winding 114, V_(ref) _(_) _(ea) represents the referencesignal 222 and R_(cs) represents the resistance of the resistor 130. Asshown in Equation 1, the parameters associated with peripheralcomponents, such as N and R_(cs), can be properly selected throughsystem design to achieve output current regulation.

For LED lighting, efficiency, power factor and total harmonic are alsoimportant. For example, efficiency is often needed to be as high aspossible (e.g., >90%), and a power factor is often needed to be greaterthan 0.9. Moreover, total harmonic distortion is often needed to be aslow as possible (e.g., <10%) for some applications. But the system 100often cannot satisfy all these needs.

Hence it is highly desirable to improve the techniques of regulatingoutput currents of power conversion systems.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for currentregulation. Merely by way of example, the invention has been applied topower conversion systems. But it would be recognized that the inventionhas a much broader range of applicability.

According to one embodiment, a system controller for regulating a powerconversion system includes a first controller terminal and a secondcontroller terminal. The first controller terminal is configured toreceive a first signal associated with an input signal for a primarywinding of a power conversation system. The second controller terminalis configured to output a drive signal to a switch to affect a firstcurrent flowing through the primary winding of the power conversionsystem, the drive signal being associated with an on-time period, theswitch being closed during the on-time period. The system controller isconfigured to adjust a duration of the on-time period based on at leastinformation associated with the first signal.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal, aramp-signal generator, and a second controller terminal. The firstcontroller terminal is configured to provide a compensation signal basedon at least information associated with a first current flowing througha primary winding of a power conversion system. The ramp-signalgenerator is configured to receive a first signal associated with thecompensation signal and generate a ramping signal based on at leastinformation associated with the first signal, the ramping signal beingassociated with a ramping slope. The second controller terminal isconfigured to output a drive signal to a switch based on at leastinformation associated with the ramping signal to affect the firstcurrent. The system controller is configured to adjust the ramping slopeof the ramping signal based on at least information associated with thecompensation signal.

According to yet another embodiment, a method for regulating a powerconversion system includes: receiving a first signal from a firstcontroller terminal, the first signal being associated with an inputsignal for a primary winding of a power conversation system; adjusting aduration of an on-time period related to a drive signal based on atleast information associated with the first signal; and outputting thedrive signal from a second controller terminal to a switch to affect afirst current flowing through the primary winding of the powerconversion system, the switch being closed during the on-time period.

According to yet another embodiment, a method for regulating a powerconversion system includes: providing a compensation signal by a firstcontroller terminal based on at least information associated with afirst current flowing through a primary winding of a power conversionsystem; generating a first signal based on at least informationassociated with the compensation signal; and processing informationassociated with the first signal. The method further includes: adjustinga ramping slope associated with a ramping signal based on at leastinformation associated with the first signal; receiving the rampingsignal; generating a drive signal based on at least informationassociated with the ramping signal; and outputting the drive signal froma second controller terminal to a switch to affect the first current.

In one embodiment, a system controller for regulating a power conversionsystem includes: a signal generator configured to receive a convertedsignal and a first compensation signal and generate a secondcompensation signal based at least in part on the converted signal andthe first compensation signal, the converted signal being associatedwith an input signal for a power conversion system, the firstcompensation signal being associated with a sensing signal related to afirst current flowing through a primary winding of the power conversionsystem; a modulation component configured to receive the secondcompensation signal and a ramping signal and generate a modulationsignal based at least in part on the second compensation signal and theramping signal; and a drive component configured to receive themodulation signal and output a drive signal based at least in part onthe modulation signal to a switch to affect the first current, the drivesignal being associated with an on-time period, the switch being closedduring the on-time period. The system controller is configured to adjusta duration of the on-time period based at least in part on the convertedsignal and the second compensation signal.

In another embodiment, a method for regulating a power conversion systemincludes: receiving a converted signal and a first compensation signal,the converted signal being associated with an input signal for a powerconversion system, the first compensation signal being associated with asensing signal related to a first current flowing through a primarywinding of the power conversion system; generating a second compensationsignal based at least in part on the converted signal and the firstcompensation signal; receiving the second compensation signal and aramping signal; generating a modulation signal based at least in part onthe second compensation signal and the ramping signal; receiving themodulation signal; and outputting a drive signal based at least in parton the modulation signal to affect the first current, the drive signalbeing associated with an on-time period. The outputting a drive signalbased at least in part on the modulation signal to affect the firstcurrent includes adjusting a duration of the on-time period based atleast in part on the converted signal and the second compensationsignal.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional power conversationsystem for LED lighting.

FIG. 2 is a simplified conventional diagram showing a controller as partof the system as shown in FIG. 1.

FIG. 3 is a simplified conventional diagram showing the current-sensingcomponent and the error amplifier as parts of the controller as shown inFIG. 2.

FIG. 4(a) is a simplified diagram showing a power conversion systemaccording to an embodiment of the present invention.

FIG. 4(b) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 4(a) according to an embodimentof the present invention.

FIG. 4(c) is a simplified timing diagram for a controller as part of apower conversion system as shown in FIG. 4(a) according to an embodimentof the present invention.

FIG. 4(d) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 4(a) according to anotherembodiment of the present invention.

FIG. 5(a) is a simplified diagram showing a power conversion systemaccording to another embodiment of the present invention.

FIG. 5(b) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 5(a) according to an embodimentof the present invention.

FIG. 5(c) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 5(a) according to anotherembodiment of the present invention.

FIG. 6(a) is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention.

FIG. 6(b) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 6(a) according to an embodimentof the present invention.

FIG. 7(a) is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention.

FIG. 7(b) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 7(a) according to an embodimentof the present invention.

FIG. 7(c) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 7(a) according to anotherembodiment of the present invention.

FIG. 8(a) is a simplified diagram showing certain components as part ofa controller as shown in FIG. 4(b), a controller as shown in FIG. 5(b),and/or a controller as shown in FIG. 7(b) according to some embodimentsof the present invention.

FIG. 8(b) is a simplified diagram showing certain components as part ofa controller as shown in FIG. 4(d), a controller as shown in FIG. 5(c),and/or a controller as shown in FIG. 7(c) according to certainembodiments of the present invention.

FIG. 8(c) is a simplified diagram showing certain components as part ofa controller as shown in FIG. 6(b) according to another embodiment ofthe present invention.

FIG. 9 is a simplified diagram showing certain components of acontroller according to yet another embodiment of the present invention.

FIG. 10(a) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 4(a) according to yet anembodiment of the present invention.

FIG. 10(b) is a simplified timing diagram for a controller as part of apower conversion system as shown in FIG. 4(a) according to anotherembodiment of the present invention.

FIG. 10(c) is a simplified diagram showing certain components of acontroller as part of a power conversion system as shown in FIG. 4(a)according to another embodiment of the present invention.

FIG. 11(a) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 5(a) according to yet anembodiment of the present invention.

FIG. 11(b) is a simplified diagram showing certain components of acontroller as part of a power conversion system as shown in FIG. 5(a)according to another embodiment of the present invention.

FIG. 12(a) is a simplified diagram showing a controller as part of apower conversion system as shown in FIG. 7(a) according to yet anembodiment of the present invention.

FIG. 12(b) is a simplified diagram showing certain components of acontroller as part of a power conversion system as shown in FIG. 7(a)according to another embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for currentregulation. Merely by way of example, the invention has been applied topower conversion systems. But it would be recognized that the inventionhas a much broader range of applicability.

FIG. 4(a) is a simplified diagram showing a power conversion systemaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The system 400 includes acontroller 402, resistors 404, 424, 426, 432, 466 and 498, capacitors406, 420, 434 and 470, a diode 408, a transformer 410 including aprimary winding 412, a secondary winding 414 and an auxiliary winding416, a power switch 428, a current sensing resistor 430, and arectifying diode 418. The controller 402 includes terminals (e.g., pins)438, 440, 442, 444, 446, 448 and 464. For example, the power switch 428includes a bipolar junction transistor. In another example, the powerswitch 428 includes a MOS transistor. In yet another example, the powerswitch 428 includes an insulated-gate bipolar transistor. The system 400provides power to an output load 422, e.g., one or more LEDs. In someembodiments, the resistor 432 is removed. For example, the system 400operates in a quasi-resonant mode.

According to one embodiment, an alternate-current (AC) input voltage 452is applied to the system 400. For example, a bulk voltage 450 (e.g., arectified voltage no smaller than 0 V) associated with the AC inputvoltage 452 is received by the resistor 404. In another example, thecapacitor 406 is charged in response to the bulk voltage 450, and avoltage 454 is provided to the controller 402 at the terminal 438 (e.g.,terminal VCC). In yet another example, if the voltage 454 is larger thana predetermined threshold voltage in magnitude, the controller 402begins to operate normally, and outputs a signal through the terminal442 (e.g., terminal GATE). In yet another example, the switch 428 isclosed (e.g., being turned on) or open (e.g., being turned off) inresponse to a drive signal 456 so that the output current 458 isregulated to be approximately constant.

According to another embodiment, the auxiliary winding 416 charges thecapacitor 406 through the diode 408 when the switch 428 is opened (e.g.,being turned off) in response to the drive signal 456 so that thecontroller 402 can operate normally. For example, a feedback signal 460is provided to the controller 402 through the terminal 440 (e.g.,terminal FB) in order to detect the end of a demagnetization process ofthe secondary winding 414 for charging or discharging the capacitor 434using an internal error amplifier in the controller 402. In anotherexample, the feedback signal 460 is provided to the controller 402through the terminal 440 (e.g., terminal FB) in order to detect thebeginning and the end of the demagnetization process of the secondarywinding 414. As an example, the capacitor 434 is charged or dischargedin response to a compensation signal 474 at the terminal 448 (e.g.,terminal COMP). In another example, the resistor 430 is used fordetecting a primary current 462 flowing through the primary winding 412,and a current-sensing signal 496 is provided to the controller 402through the terminal 444 (e.g., terminal CS) to be processed during eachswitching cycle. In yet another example, peak magnitudes of thecurrent-sensing signal 496 are sampled and provided to the internalerror amplifier. In yet another example, the capacitor 434 is coupled toan output terminal of the internal error amplifier. In yet anotherexample, the capacitor 420 is used to maintain an output voltage 468.

According to yet another embodiment, the bulk voltage 450 is sensed bythe controller 402 through the terminal 464 (e.g., terminal VAC). Forexample, the controller 402 includes a ramp-signal generator whichgenerates a ramping signal, and the controller 402 is configured tochange the ramping slope of the ramping signal based on at leastinformation associated with a signal 472 related to the bulk voltage450. In another example, an on-time period associated with the drivesignal 456 varies based on at least information associated with thesignal 450. As an example, the duration of the on-time period increaseswhen the bulk voltage 450 is at a peak magnitude. In another example,the duration of the on-time period decreases when the bulk voltage 450is at a valley magnitude. The signal 472 is determined according to thefollowing equation:

$\begin{matrix}{{VAC} = {\frac{R_{9}}{R_{8} + R_{9}} \times V_{bulk}}} & \left( {{Equation}\mspace{14mu} 2} \right) \\{V_{bulk} = {{{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}}.}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

where VAC represents the signal 472, V_(bulk) represents the bulkvoltage 450, R₈ represents a resistance of the resistor 466, and R₉represents a resistance of the resistor 498. In addition, A represents amagnitude, ω represents a frequency, and φ represents a phase angle. Insome embodiments, the controller is configured to adjust the rampingsignal based on information associated with both the signal 472 and thecompensation signal 474. In certain embodiments, the controller 402 isconfigured to adjust the ramping slope of the ramping signal based oninformation associated with the signal 472 or the compensation signal474.

FIG. 4(b) is a simplified diagram showing the controller 402 as part ofthe power conversion system 400 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 402 includes a ramp-signal generator 602, an under-voltagelock-out (UVLO) component 604, a modulation component 606, a logiccontroller 608, a driving component 610, a demagnetization detector 612,an error amplifier 616, a current-sensing-and-sample/hold component 614,a jittering-signal generator 699, and voltage-to-current-conversioncomponents 640 and 642.

According to one embodiment, the UVLO component 604 detects the signal454 and outputs a signal 618. For example, if the signal 454 is largerthan a first predetermined threshold in magnitude, the controller 402begins to operate normally. If the signal 454 is smaller than a secondpredetermined threshold in magnitude, the controller 402 is turned off.In another example, the second predetermined threshold is smaller thanthe first predetermined threshold in magnitude. In yet another example,the error amplifier 616 receives a signal 620 from thecurrent-sensing-and-sample/hold component 614 and a reference signal622, and the signal 474 is provided to the modulation component 606 andthe voltage-to-current-conversion component 642. As an example, thevoltage-to-current-conversion component 640 receives the signal 472 andoutputs a signal 636 to the ramp-signal generator 602. In anotherexample, the ramp-signal generator 602 also receives a current signal694 and a jittering signal 697 (e.g., a jittering current) generated bythe jittering-signal generator 699 and generates a ramping signal 628.

According to another embodiment, the jittering current 697 flows fromthe jittering-signal generator 699 to the ramp-signal generator 602. Forexample, the jittering current 697 flows from the ramp-signal generator602 to the jittering-signal generator 699. In another example, themodulation component 606 receives the ramping signal 628 and outputs amodulation signal 626. For example, the signal 628 increases, linearlyor non-linearly, to a peak magnitude during each switching period. Thelogic controller 608 processes the modulation signal 626 and outputs acontrol signal 630 to the current-sensing-and-sample/hold component 614and the driving component 610.

According to yet another embodiment, the current-sensing-and-sample/holdcomponent 614 samples the current sensing signal 496 in response to thecontrol signal 630 and then holds the sampled signal until thecurrent-sensing-and-sample/hold component 614 samples again the currentsensing signal 496. For example, the driving component 610 generates asignal 656 related to the drive signal 456 to affect the switch 428. Asan example, the demagnetization detector 612 detects the feedback signal460 and outputs a demagnetization signal 632 for determining the end ofthe demagnetization process of the secondary winding 414. As anotherexample, the demagnetization detector 612 detects the feedback signal460 and outputs the demagnetization signal 632 for determining thebeginning and the end of the demagnetization process of the secondarywinding 414. In yet another example, the demagnetization detector 612outputs a trigger signal 698 to the logic controller 608 to start a nextcycle (e.g., corresponding to a next switching period). In yet anotherexample, when the signal 656 is at a logic high level, the signal 456 isat a logic high level, and when the signal 656 is at a logic low level,the signal 456 is at a logic low level. In yet another example, thecapacitor 434 is coupled to the terminal 448 and forms, together withthe error amplifier 616, an integrator or a low-pass filter. In yetanother example, the error amplifier 616 is a transconductance amplifierand outputs a current which is proportional to a difference between thereference signal 622 and the signal 620. In yet another example, theerror amplifier 616 together with the capacitor 434 generates the signal474 which is a voltage signal. In yet another example, the ramping slopeof the ramping signal 628 is modulated in response to the jitteringsignal 697.

In some embodiments, the jittering signal 697 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 697is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 656 is associated with multiple modulation cyclescorresponding to a modulation frequency (e.g., not constant) related toa modulation period (e.g., not constant). In another example, the systemcontroller 402 changes the ramping slope associated with the rampingsignal 628 based on at least information associated with the jitteringsignal 628 so that, within a same jittering cycle of the multiplejittering cycles, the ramping slope is changed (e.g., increased, ordecreased) by different magnitudes corresponding to different modulationcycles respectively. In yet another example, the ramping slope ischanged during different modulation cycles adjacent to each other. Inyet another example, the ramping slope is changed during differentmodulation cycles not adjacent to each other. In yet another example,the system controller 402 adjusts the modulation frequency based on atleast information associated with the changed ramping slope.

In certain embodiments, the jittering signal 697 corresponds to a random(e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 402 changes the rampingslope associated with the ramping signal 628 based on at leastinformation associated with the random jittering signal 628 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 402 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

In some embodiments, the signal 636 represents a current and is used foradjusting a ramping slope associated with the ramping signal 628. Incertain embodiments, the signal 638 represents a current and is used foradjusting the ramping slope associated with the ramping signal 628. Forexample, information associated with both the signal 636 and the signal638 is used for adjusting the ramping slope associated with the rampingsignal 628, so as to adjust the duration of an on-time period associatedwith the drive signal 456. In another example, the current 636 flowsfrom the voltage-to-current-conversion component 640 to the ramp-signalgenerator 602. In yet another example, the current 636 flows from theramp-signal generator 602 to the voltage-to-current-conversion component640. In yet another example, the current 638 flows from thevoltage-to-current-conversion component 642 to the ramp-signal generator602. In yet another example, the current 638 flows from the ramp-signalgenerator 602 to the voltage-to-current-conversion component 642.

FIG. 4(c) is a simplified timing diagram for the controller 402 as partof the power conversion system 400 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thewaveform 902 represents the signal 626 as a function of time, thewaveform 904 represents the signal 656 as a function of time, the waveform 906 represents the demagnetization signal 632 as a function oftime, the waveform 908 represents the trigger signal 698 as a functionof time, and the waveform 910 represents the ramping signal 628 as afunction of time.

An on-time period and an off-time period associated with the signal 656are shown in FIG. 4(c). The on-time period begins at a time t₃ and endsat a time t₅, and the off-time period begins at the time t₅ and ends ata time t₇. For example, t₀≦t₁≦t₂≦t₃≦t₄≦t₅≦t₆≦t₇.

According to one embodiment, at t₀, the demagnetization signal 632changes from the logic low level to the logic high level. For example,the demagnetization detector 612 generates a pulse (e.g., between t₀ andt₂) in the trigger signal 698 to trigger a new cycle. As an example, theramping signal 628 begins to increases from a magnitude 912 to amagnitude 914 (e.g., at t₄). In another example, at t₁, the signal 626changes from the logic low level to the logic high level. After a shortdelay, the signal 656 changes (e.g., at t₃) from the logic low level tothe logic high level, and in response the switch 428 is turned on. Inyet another example, at t₄, the signal 626 changes from the logic highlevel to the logic low level, and the ramping signal 628 decreases fromthe magnitude 914 to the magnitude 912. After a short delay, the signal656 changes (e.g., at t₅) from the logic high level to the logic lowlevel, and in response, the switch 428 is turned off. As an example, att₆, the demagnetization signal 632 changes from the logic low level tothe logic high level which indicates a beginning of a demagnetizationprocess. In another example, at t₇, the demagnetization signal 632changes from the logic high level to the logic low level which indicatesan end of the demagnetization process. In yet another example, thedemagnetization detector 612 generates another pulse in the triggersignal 698 to start a next cycle. In yet another example, the magnitude914 of the ramping signal 628 is associated with the magnitude of thesignal 474.

According to another embodiment, the magnitude change of the rampingsignal 628 during the on-time period is determined as follows:

ΔV _(ramp) =V _(comp) −V _(ref) _(_) ₁=slope×T _(on)   (Equation 4)

where ΔV_(ramp) represents the magnitude changes of the ramping signal628, V_(comp) represents the signal 474, V_(ref) _(_) _(i) represents apredetermined voltage magnitude, slope represents a ramping slopeassociated with the ramping signal 628, and T_(on) represents theduration of the on-time period. For example, V_(ref) _(_) ₁ correspondsto a minimum magnitude of the ramping signal 628. Based on Equation 4,the duration of the on-time period is determined as follows:

$\begin{matrix}{T_{on} = \frac{V_{comp} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

As shown in Equation 5, for a given compensation signal (e.g., thesignal 474), the duration of the on-time period is determined by theramping slope of the ramping signal 628. In some embodiments, theramping slope of the ramping signal 628 is adjusted according to thesignal 636 and the signal 638, so that the duration of the on-timeperiod associated with the drive signal 456 is adjusted. For example,adjusting the ramping slope of the ramping signal 628 to change theduration of the on-time period is applicable to power conversion systemswith a buck-boost topology operated in a quasi-resonant (QR) mode. Inanother example, a slope of the waveform 910 between t₁ and t₄corresponds to the ramping slope of the ramping signal 628.

As discussed above and further emphasized here, FIGS. 4(b) and 4(c) aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, thevoltage-to-current-conversion component 642 is removed from thecontroller 402, as shown in FIG. 4(d).

FIG. 4(d) is a simplified diagram showing the controller 402 as part ofthe power conversion system 400 according to another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 402 includes a ramp-signal generator 1402, an under-voltagelock-out (UVLO) component 1404, a modulation component 1406, a logiccontroller 1408, a driving component 1410, a demagnetization detector1412, an error amplifier 1416, a current-sensing-and-sample/holdcomponent 1414, a jittering-signal generator 1499, and avoltage-to-current-conversion component 1440.

In some embodiments, the ramp-signal generator 1402 receives a currentsignal 1494, a jittering signal 1497 (e.g., a jittering current)generated by the jittering-signal generator 1499 and a signal 1436 fromthe voltage-to-current-conversion component 1440 and outputs a rampingsignal 1428. For example, the jittering current 1497 flows from thejittering-signal generator 1499 to the ramp-signal generator 1402. Inanother example, the jittering current 1497 flows from the ramp-signalgenerator 1402 to the jittering-signal generator 1499. For example, aramping slope associated with the ramping signal 1428 is adjusted basedon at least information associated with the signal 1436 that is relatedto the bulk voltage 450. The operations of other components in FIG. 4(d)are similar to what are described in FIG. 4(b). For example, the timingdiagram for the controller 402 as part of the system 400 is similar towhat is shown in FIG. 4(c). As an example, the signal 1436 represents acurrent. In another example, the current 1436 flows from thevoltage-to-current-conversion component 1440 to the ramp-signalgenerator 1402. In yet another example, the current 1436 flows from theramp-signal generator 1402 to the voltage-to-current-conversioncomponent 1440. In yet another example, the ramping slope of the rampingsignal 1428 is modulated in response to the jittering signal 1497.

In certain embodiments, the jittering signal 1497 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 1497is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 1456 is associated with multiple modulationcycles corresponding to a modulation frequency (e.g., not constant)related to a modulation period (e.g., not constant). In another example,the system controller 402 changes the ramping slope associated with theramping signal 1428 based on at least information associated with thejittering signal 1428 so that, within a same jittering cycle of themultiple jittering cycles, the ramping slope is changed (e.g.,increased, or decreased) by different magnitudes corresponding todifferent modulation cycles respectively. In yet another example, theramping slope is changed during different modulation cycles adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles not adjacent to each other. In yet anotherexample, the system controller 402 adjusts the modulation frequencybased on at least information associated with the changed ramping slope.

In certain embodiments, the jittering signal 1497 corresponds to arandom (e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 402 changes the rampingslope associated with the ramping signal 1428 based on at leastinformation associated with the random jittering signal 1428 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 402 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

As discussed above and further emphasized here, FIG. 4(a), FIG. 4(b),FIG. 4(c), and/or FIG. 4(d) are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,the ramping slope associated with an internal ramping signal in acontroller is adjusted using a current signal associated with a bulkvoltage, as shown in FIG. 5(a), FIG. 5(b), and FIG. 5(c).

FIG. 5(a) is a simplified diagram showing a power conversion systemaccording to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The system 800 includes acontroller 802, resistors 804, 824, 826, 832 and 866, capacitors 806,820, and 834, a diode 808, a transformer 810 including a primary winding812, a secondary winding 814 and an auxiliary winding 816, a powerswitch 828, a current sensing resistor 830, and a rectifying diode 818.The controller 802 includes terminals (e.g., pins) 838, 840, 842, 844,846, 848 and 864. For example, the power switch 828 includes a bipolarjunction transistor. In another example, the power switch 828 includes aMOS transistor. In yet another example, the power switch 828 includes aninsulated-gate bipolar transistor. The system 800 provides power to anoutput load 822, e.g., one or more LEDs. In some embodiments, theresistor 832 is removed. For example, the system 800 operates in aquasi-resonant mode.

According to one embodiment, an alternate-current (AC) input voltage 852is applied to the system 800. For example, a bulk voltage 850 (e.g., arectified voltage no smaller than 0 V) associated with the AC inputvoltage 852 is received by the resistor 804. In another example, thecapacitor 806 is charged in response to the bulk voltage 850, and avoltage 854 is provided to the controller 802 at the terminal 838 (e.g.,terminal VCC). In yet another example, if the voltage 854 is larger thana predetermined threshold voltage in magnitude, the controller 802begins to operate normally, and outputs a signal through the terminal842 (e.g., terminal GATE). In yet another example, the switch 828 isclosed (e.g., being turned on) or open (e.g., being turned off) inresponse to a drive signal 856 so that the output current 858 isregulated to be approximately constant.

According to another embodiment, the auxiliary winding 816 charges thecapacitor 806 through the diode 808 when the switch 828 is opened (e.g.,being turned off) in response to the drive signal 856 so that thecontroller 802 can operate normally. For example, a feedback signal 860is provided to the controller 802 through the terminal 840 (e.g.,terminal FB) in order to detect the end of a demagnetization process ofthe secondary winding 814 for charging or discharging the capacitor 834using an internal error amplifier in the controller 802. In anotherexample, the feedback signal 860 is provided to the controller 802through the terminal 840 (e.g., terminal FB) in order to detect thebeginning and the end of the demagnetization process of the secondarywinding 814. As an example, the capacitor 834 is charged or dischargedin response to a compensation signal 874 at the terminal 848 (e.g.,terminal COMP). In another example, the resistor 830 is used fordetecting a primary current 862 flowing through the primary winding 812,and a current-sensing signal 896 is provided to the controller 802through the terminal 844 (e.g., terminal CS) to be processed during eachswitching cycle. In yet another example, peak magnitudes of thecurrent-sensing signal 896 are sampled and provided to the internalerror amplifier. In yet another example, the capacitor 834 is coupled toan output terminal of the internal error amplifier. In yet anotherexample, the capacitor 820 is used to maintain an output voltage 868.

According to yet another embodiment, the bulk voltage 850 is sensed bythe controller 802 through the terminal 864 (e.g., terminal IAC). Forexample, the controller 802 includes a ramp-signal generator whichgenerates a ramping signal, and the controller 802 is configured tochange the ramping slope of the ramping signal based on at leastinformation associated with a signal 872 related to the bulk voltage850. In another example, an on-time period associated with the drivesignal 856 varies based on at least information associated with thesignal 850. As an example, the duration of the on-time period increaseswhen the bulk voltage 850 is at a peak magnitude. In another example,the duration of the on-time period decreases when the bulk voltage 850is at a valley magnitude. The signal 872 is determined according to thefollowing equation:

$\begin{matrix}{I_{ac} = {\mu \times \frac{V_{bulk}}{R_{8}}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where I_(ac) represents the signal 872, V_(bulk) represents the bulkvoltage 850, R₈ represents a resistance of the resistor 866, and μrepresents a constant.

In some embodiments, the controller is configured to adjust the rampingsignal based on information associated with both the signal 872 and thecompensation signal 874. In certain embodiments, the controller isconfigured to adjust the ramping signal based on information associatedwith the signal 872 or the compensation signal 874.

FIG. 5(b) is a simplified diagram showing the controller 802 as part ofthe power conversion system 800 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 802 includes a ramp-signal generator 1002, an under-voltagelock-out (UVLO) component 1004, a modulation component 1006, a logiccontroller 1008, a driving component 1010, a demagnetization detector1012, an error amplifier 1016, a current-sensing-and-sample/holdcomponent 1014, another current-sensing component 1040, ajittering-signal generator 1099, and a voltage-to-current-conversioncomponents 1042.

According to one embodiment, the UVLO component 1004 detects the signal854 and outputs a signal 1018. For example, if the signal 854 is largerthan a first predetermined threshold in magnitude, the controller 802begins to operate normally. If the signal 854 is smaller than a secondpredetermined threshold in magnitude, the controller 802 is turned off.In yet another example, the second predetermined threshold is smallerthan the first predetermined threshold in magnitude. In yet anotherexample, the error amplifier 1016 receives a signal 1020 from thecurrent-sensing-and-sample/hold component 1014 and a reference signal1022, and the signal 874 is provided to the modulation component 1006and the voltage-to-current-conversion component 1042. As an example, thecurrent-sensing component 1040 receives the signal 872 and outputs asignal 1036 to the ramp-signal generator 1002 which also receives acurrent signal 1094 and a jittering signal 1097 (e.g., a jitteringcurrent) generated by the jittering-signal generator 1099. In anotherexample, the jittering current 1097 flows from the jittering-signalgenerator 1099 to the ramp-signal generator 1002. In yet anotherexample, the jittering current 1097 flows from the ramp-signal generator1002 to the jittering-signal generator 1099. In yet another example, themodulation component 1006 receives a ramping signal 1028 from theramp-signal generator 1002 and outputs a modulation signal 1026. Forexample, the signal 1028 increases, linearly or non-linearly, to a peakmagnitude during each switching period. The logic controller 1008processes the modulation signal 1026 and outputs a control signal 1030to the current-sensing-and-sample/hold component 1014 and the drivingcomponent 1010. For example, the driving component 1010 generates asignal 1056 related to the drive signal 856 to affect the switch 828. Asan example, the demagnetization detector 1012 detects the feedbacksignal 860 and outputs a demagnetization signal 1032 for determining theend of the demagnetization process of the secondary winding 814. Asanother example, the demagnetization detector 1012 detects the feedbacksignal 860 and outputs the demagnetization signal 1032 for determiningthe beginning and the end of the demagnetization process of thesecondary winding 814. In another example, the demagnetization detector1012 outputs a trigger signal 1098 to the logic controller 1008 to starta next modulation cycle. In yet another example, when the signal 1056 isat a logic high level, the signal 856 is at a logic high level, and whenthe signal 1056 is at a logic low level, the signal 856 is at a logiclow level. In yet another example, the ramping slope of the rampingsignal 1028 is modulated in response to the jittering signal 1097.

In some embodiments, the jittering signal 1097 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 1097is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 1056 is associated with multiple modulationcycles corresponding to a modulation frequency (e.g., not constant)related to a modulation period (e.g., not constant). In another example,the system controller 802 changes the ramping slope associated with theramping signal 1028 based on at least information associated with thejittering signal 1028 so that, within a same jittering cycle of themultiple jittering cycles, the ramping slope is changed (e.g.,increased, or decreased) by different magnitudes corresponding todifferent modulation cycles respectively. In yet another example, theramping slope is changed during different modulation cycles adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles not adjacent to each other. In yet anotherexample, the system controller 802 adjusts the modulation frequencybased on at least information associated with the changed ramping slope.

In certain embodiments, the jittering signal 1097 corresponds to arandom (e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 802 changes the rampingslope associated with the ramping signal 1028 based on at leastinformation associated with the random jittering signal 1028 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 802 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

In some embodiments, the signal 1036 represents a current and is usedfor adjusting a ramping slope associated with the ramping signal 1028.In certain embodiments, the signal 1038 represents a current and is usedfor adjusting the ramping slope associated with the ramping signal 1028.For example, information associated with both the signal 1036 and thesignal 1038 is used for adjusting the ramping slope associated with theramping signal 1028, so as to adjust the duration of an on-time periodassociated with the drive signal 856. For example, the timing diagramfor the controller 802 as part of the system 800 is similar to what isshown in FIG. 4(c). In another example, the current 1036 flows from thecurrent-sensing component 1040 to the ramp-signal generator 1002. In yetanother example, the current 1036 flows from the ramp-signal generator1002 to the current-sensing component 1040. In yet another example, thecurrent 1038 flows from the voltage-to-current-conversion component 1042to the ramp-signal generator 1002. In yet another example, the current1038 flows from the ramp-signal generator 1002 to thevoltage-to-current-conversion component 1042.

FIG. 5(c) is a simplified diagram showing the controller 802 as part ofthe power conversion system 800 according to another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 802 includes a ramp-signal generator 1502, an under-voltagelock-out (UVLO) component 1504, a modulation component 1506, a logiccontroller 1508, a driving component 1510, a demagnetization detector1512, an error amplifier 1516, a current-sensing-and-sample/holdcomponent 1514, a jittering-signal generator 1599, and anothercurrent-sensing component 1540.

In some embodiments, the ramp-signal generator 1502 receives a currentsignal 1594, a jittering signal 1597 (e.g., a jittering current)generated by the jittering-signal generator 1599, and a signal 1536 fromthe current-sensing component 1540 and outputs a ramping signal 1528. Asan example, the jittering current 1597 flows from the jittering-signalgenerator 1599 to the ramp-signal generator 1502. As another example,the jittering current 1597 flows from the ramp-signal generator 1502 tothe jittering-signal generator 1599. For example, a ramping slopeassociated with the ramping signal 1528 is adjusted based on at leastinformation associated with the signal 1536 that is related to a currentsignal associated with the bulk voltage 850. The operations of othercomponents in FIG. 5(c) are similar to what are described in FIG. 5(b).As an example, the signal 1536 represents a current. In another example,the current 1536 flows from the current-sensing component 1540 to theramp-signal generator 1502. In yet another example, the current 1536flows from the ramp-signal generator 1502 to the current-sensingcomponent 1540. In yet another example, the ramping slope of the rampingsignal 1528 is modulated in response to the jittering signal 1597.

In some embodiments, the jittering signal 1597 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 1597is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 1556 is associated with multiple modulationcycles corresponding to a modulation frequency (e.g., not constant)related to a modulation period (e.g., not constant). In another example,the system controller 802 changes the ramping slope associated with theramping signal 1528 based on at least information associated with thejittering signal 1528 so that, within a same jittering cycle of themultiple jittering cycles, the ramping slope is changed (e.g.,increased, or decreased) by different magnitudes corresponding todifferent modulation cycles respectively. In yet another example, theramping slope is changed during different modulation cycles adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles not adjacent to each other. In yet anotherexample, the system controller 802 adjusts the modulation frequencybased on at least information associated with the changed ramping slope.

In certain embodiments, the jittering signal 1597 corresponds to arandom (e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 802 changes the rampingslope associated with the ramping signal 1528 based on at leastinformation associated with the random jittering signal 1528 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 802 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

As discussed above and further emphasized here, FIG. 4(a), FIG. 4(b),FIG. 5(a), and/or FIG. 5(b) are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,a terminal (e.g., the terminal 464, the terminal 864) configured toreceive signals related to a bulk voltage (e.g., the bulk voltage 450,the bulk voltage 850) is removed from a controller (e.g., the controller402, the controller 802) for a power conversion system, as shown in FIG.6(a) and FIG. 6(b).

FIG. 6(a) is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The system 500 includes acontroller 502, resistors 504, 524, 526 and 532, capacitors 506, 520 and534, a diode 508, a transformer 510 including a primary winding 512, asecondary winding 514 and an auxiliary winding 516, a power switch 528,a current sensing resistor 530, and a rectifying diode 518. Thecontroller 502 includes terminals (e.g., pins) 538, 540, 542, 544, 546and 548. For example, the power switch 528 is a bipolar junctiontransistor. In another example, the power switch 528 is a MOStransistor. In yet another example, the power switch 528 includes aninsulated-gate bipolar transistor. The system 500 provides power to anoutput load 522, e.g., one or more LEDs. In some embodiments, theresistor 532 is removed. For example, the system 500 operates in aquasi-resonant mode.

According to one embodiment, an alternate-current (AC) input voltage 552is applied to the system 500. For example, a bulk voltage 550 (e.g., arectified voltage no smaller than 0 V) associated with the AC inputvoltage 552 is received by the resistor 504. In another example, thecapacitor 506 is charged in response to the bulk voltage 550, and avoltage 554 is provided to the controller 502 at the terminal 538 (e.g.,terminal VCC). In yet another example, if the voltage 554 is larger thana predetermined threshold voltage in magnitude, the controller 502begins to operate normally, and outputs a signal through the terminal542 (e.g., terminal GATE). In yet another example, the switch 528 isclosed (e.g., being turned on) or open (e.g., being turned off) inresponse to a drive signal 556 so that the output current 558 isregulated to be approximately constant.

According to another embodiment, the auxiliary winding 516 charges thecapacitor 506 through the diode 508 when the switch 528 is opened (e.g.,being turned off) in response to the drive signal 556 so that thecontroller 502 can operate normally. For example, a feedback signal 560is provided to the controller 502 through the terminal 540 (e.g.,terminal FB) in order to detect the end of a demagnetization process ofthe secondary winding 514 for charging or discharging the capacitor 534using an internal error amplifier in the controller 502. In anotherexample, the feedback signal 560 is provided to the controller 502through the terminal 540 (e.g., terminal FB) in order to detect thebeginning and the end of the demagnetization process of the secondarywinding 514. As an example, the capacitor 534 is charged or dischargedin response to a compensation signal 574 provided at the terminal 548(e.g., terminal COMP). In another example, the resistor 530 is used fordetecting a primary current 562 flowing through the primary winding 512,and a current-sensing signal 564 is provided to the controller 502through the terminal 544 (e.g., terminal CS) to be processed during eachswitching cycle. In yet another example, peak magnitudes of thecurrent-sensing signal 564 are sampled and provided to the internalerror amplifier. In yet another example, the capacitor 520 is used tomaintain an output voltage 568. In some embodiments, the controller 502includes a ramp-signal generator which generates a ramping signal, andthe controller 502 is configured to change the ramping slope of theramping signal based on at least information associated with thecompensation signal 574.

FIG. 6(b) is a simplified diagram showing the controller 502 as part ofthe power conversion system 500 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 502 includes a ramp-signal generator 702, an under-voltagelock-out (UVLO) component 704, a modulation component 706, a logiccontroller 708, a driving component 710, a demagnetization detector 712,an error amplifier 716, a current-sensing-and-sample/hold component 714,a jittering-signal generator 799, and a voltage-to-current-conversioncomponent 742.

According to one embodiment, the UVLO component 704 detects the signal554 and outputs a signal 718. For example, if the signal 554 is largerthan a first predetermined threshold in magnitude, the controller 502begins to operate normally. If the signal 554 is smaller than a secondpredetermined threshold in magnitude, the controller 502 is turned off.In another example, the second predetermined threshold is smaller thanthe first predetermined threshold in magnitude. In yet another example,the error amplifier 716 receives a signal 720 from thecurrent-sensing-and-sample/hold component 714 and a reference signal 722and the compensation signal 574 is provided to the modulation component706 and the voltage-to-current-conversion component 742. In yet anotherexample, the voltage-to-current-conversion component 742 receives thesignal 574 and outputs a signal 738 to the ramp-signal generator 702which also receives a current signal 794 and a jittering signal 797(e.g., a jittering current) generated by the jittering-signal generator799. In yet another example, the jittering current 797 flows from thejittering-signal generator 799 to the ramp-signal generator 702. In yetanother example, the jittering current 797 flows from the ramp-signalgenerator 702 to the jittering-signal generator 799. In yet anotherexample, the modulation component 706 receives a ramping signal 728 fromthe ramp-signal generator 702 and outputs a modulation signal 726. Forexample, the signal 728 increases, linearly or non-linearly, to a peakmagnitude during each switching period. In another example, the logiccontroller 708 processes the modulation signal 726 and outputs a controlsignal 730 to the current-sensing-and-sample/hold component 714 and thedriving component 710. In yet another example, the driving component 710generates a signal 756 associated with the drive signal 556 to affectthe switch 528. As an example, the demagnetization detector 712 detectsthe feedback signal 560 and outputs a signal 732 for determining the endof the demagnetization process of the secondary winding 514. As anotherexample, the demagnetization detector 712 detects the feedback signal560 and outputs the signal 732 for determining the beginning and the endof the demagnetization process of the secondary winding 514. In anotherexample, the demagnetization detector 712 outputs a trigger signal 798to the logic controller 708 to start a next cycle (e.g., correspondingto a next switching period). In yet another example, when the signal 756is at a logic high level, the signal 556 is at a logic high level, andwhen the signal 756 is at a logic low level, the signal 556 is at alogic low level. In yet another example, the ramping slope of theramping signal 728 is modulated in response to the jittering signal 797.

In some embodiments, the jittering signal 797 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 797is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 756 is associated with multiple modulation cyclescorresponding to a modulation frequency (e.g., not constant) related toa modulation period (e.g., not constant). In another example, the systemcontroller 502 changes the ramping slope associated with the rampingsignal 728 based on at least information associated with the jitteringsignal 728 so that, within a same jittering cycle of the multiplejittering cycles, the ramping slope is changed (e.g., increased, ordecreased) by different magnitudes corresponding to different modulationcycles respectively. In yet another example, the ramping slope ischanged during different modulation cycles adjacent to each other. Inyet another example, the ramping slope is changed during differentmodulation cycles not adjacent to each other. In yet another example,the system controller 502 adjusts the modulation frequency based on atleast information associated with the changed ramping slope.

In certain embodiments, the jittering signal 797 corresponds to a random(e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 502 changes the rampingslope associated with the ramping signal 728 based on at leastinformation associated with the random jittering signal 728 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 502 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

In some embodiments, the signal 738 represents a current and is used foradjusting the ramping slope associated with the ramping signal 728. Forexample, information associated with the signal 738 is used foradjusting the ramping slope associated with the ramping signal 728, soas to adjust the duration of an on-time period associated with the drivesignal 556. For example, the timing diagram for the controller 502 aspart of the system 500 is similar to what is shown in FIG. 4(c). Inanother example, the current 738 flows from thevoltage-to-current-conversion component 742 to the ramp-signal generator702. In yet another example, the current 738 flows from the ramp-signalgenerator 702 to the voltage-to-current-conversion component 742.

FIG. 7(a) is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The system 1100 includes acontroller 1102, resistors 1104, 1124, 1126 and 1132, capacitors 1106,1120 and 1134, a diode 1108, a transformer 1110 including a primarywinding 1112, a secondary winding 1114 and an auxiliary winding 1116, apower switch 1128, a current sensing resistor 1130, and a rectifyingdiode 1118. The controller 1102 includes terminals (e.g., pins) 1138,1140, 1142, 1144, 1146 and 1148. For example, the power switch 1128 is abipolar junction transistor. In another example, the power switch 1128is a MOS transistor. In yet another example, the power switch 1128includes an insulated-gate bipolar transistor. The system 1100 providespower to an output load 1122, e.g., one or more LEDs. In someembodiments, the resistor 1132 is removed. For example, the system 1100operates in a quasi-resonant mode.

According to one embodiment, an alternate-current (AC) input voltage1152 is applied to the system 1100. For example, a bulk voltage 1150(e.g., a rectified voltage no smaller than 0 V) associated with the ACinput voltage 1152 is received by the resistor 1104. In another example,the capacitor 1106 is charged in response to the bulk voltage 1150, anda voltage 1154 is provided to the controller 1102 at the terminal 1138(e.g., terminal VCC). In yet another example, if the voltage 1154 islarger than a predetermined threshold voltage in magnitude, thecontroller 1102 begins to operate normally, and outputs a signal throughthe terminal 1142 (e.g., terminal GATE). In yet another example, theswitch 1128 is closed (e.g., being turned on) or open (e.g., beingturned off) in response to a drive signal 1156 so that the outputcurrent 1158 is regulated to be approximately constant.

According to another embodiment, the auxiliary winding 1116 charges thecapacitor 1106 through the diode 1108 when the switch 1128 is opened(e.g., being turned off) in response to the drive signal 1156 so thatthe controller 1102 can operate normally. For example, a signal 1160 isprovided at the terminal 1140 (e.g., terminal FB). In another example,during an on-time period associated with the drive signal 1156, thesignal 1198 is related to the bulk voltage 1150 through thetransformer's coupling. In yet another example, the bulk voltage 1150 issensed through the terminal 1140 (e.g., terminal FB). In yet anotherexample, during an off-time period associated with the drive signal1156, the signal 1160 is related to an output voltage 1168 and is usedto detect the end of a demagnetization process of the secondary winding1114 for charging or discharging the capacitor 1134 using an internalerror amplifier in the controller 1102. As an example, the capacitor1134 is charged or discharged in response to a compensation signal 1174provided at the terminal 1148 (e.g., terminal COMP). For example, theresistor 1130 is used for detecting a primary current 1162 flowingthrough the primary winding 1112, and a current-sensing signal 1164 isprovided to the controller 1102 through the terminal 1144 (e.g.,terminal CS) to be processed during each switching cycle. In yet anotherexample, peak magnitudes of the current-sensing signal 1164 are sampledand provided to the internal error amplifier. In yet another example,the capacitor 1120 is used to maintain the output voltage 1168. In someembodiments, the controller 1102 includes a ramp-signal generator whichgenerates a ramping signal, and the controller 1102 is configured tochange the ramping slope of the ramping signal based on at leastinformation associated with the signal 1160 and the compensation signal1174.

FIG. 7(b) is a simplified diagram showing the controller 1102 as part ofthe power conversion system 1100 according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 1102 includes a ramp-signal generator 1202, an under-voltagelock-out (UVLO) component 1204, a modulation component 1206, a logiccontroller 1208, a driving component 1210, a demagnetization detector1212, an error amplifier 1216, a current-sensing-and-sample/holdcomponent 1214, another current-sensing component 1240, ajittering-signal generator 1299, and a voltage-to-current-conversioncomponent 1242.

According to one embodiment, the UVLO component 1204 detects the signal1154 and outputs a signal 1218. For example, if the signal 1154 islarger than a first predetermined threshold in magnitude, the controller1102 begins to operate normally. If the signal 1154 is smaller than asecond predetermined threshold in magnitude, the controller 1102 isturned off In another example, the first predetermined threshold islarger than the second predetermined threshold in magnitude. In yetanother example, the error amplifier 1216 receives a signal 1220 fromthe current-sensing-and-sample/hold component 1214 and a referencesignal 1222 and the compensation signal 1174 is provided to themodulation component 1206 and the voltage-to-current-conversioncomponent 1242. In yet another example, thevoltage-to-current-conversion component 1242 receives the signal 1174and outputs a signal 1238 to the ramp-signal generator 1202 which alsoreceives a current signal 1294 and a jittering signal 1297 (e.g., ajittering current) generated by the jittering-signal generator 1299. Inyet another example, the jittering current 1297 flows from thejittering-signal generator 1299 to the ramp-signal generator 1202. Inyet another example, the jittering current 1297 flows from theramp-signal generator 1202 to the jittering-signal generator 1299. Inyet another example, the current-sensing component 1240 outputs a signal1236 to the ramp-signal generator 1202 in response to a current signal1296 associated with the terminal 1140 (e.g., terminal FB). As anexample, the current signal 1296 is related to the bulk voltage 1150during the on-time period associated with the driving signal 1156. Inyet another example, the ramping slope of the ramping signal 1228 ismodulated in response to the jittering signal 1297.

In some embodiments, the jittering signal 1297 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 1297is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 1256 is associated with multiple modulationcycles corresponding to a modulation frequency (e.g., not constant)related to a modulation period (e.g., not constant). In another example,the system controller 1102 changes the ramping slope associated with theramping signal 1228 based on at least information associated with thejittering signal 1228 so that, within a same jittering cycle of themultiple jittering cycles, the ramping slope is changed (e.g.,increased, or decreased) by different magnitudes corresponding todifferent modulation cycles respectively. In yet another example, theramping slope is changed during different modulation cycles adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles not adjacent to each other. In yet anotherexample, the system controller 1102 adjusts the modulation frequencybased on at least information associated with the changed ramping slope.

In certain embodiments, the jittering signal 1297 corresponds to arandom (e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 1102 changes the rampingslope associated with the ramping signal 1228 based on at leastinformation associated with the random jittering signal 1228 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 1102 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

According to another embodiment, the modulation component 1206 receivesa ramping signal 1228 from the ramp-signal generator 1202 and outputs amodulation signal 1226. For example, the signal 1228 increases, linearlyor non-linearly, to a peak magnitude during each switching period. Inanother example, the logic controller 1208 processes the modulationsignal 1226 and outputs a control signal 1230 to thecurrent-sensing-and-sample/hold component 1214 and the driving component1210. In yet another example, the driving component 1210 generates asignal 1256 associated with the drive signal 1156 to affect the switch1128. As an example, the demagnetization detector 1212 detects thesignal 1160 and outputs a signal 1232 (e.g., during an off-time periodassociated with the drive signal 1156) for determining the end of thedemagnetization process of the secondary winding 1114. As anotherexample, the demagnetization detector 1212 detects the signal 1160 andoutputs the signal 1232 (e.g., during the off-time period associatedwith the drive signal 1156) for determining the beginning and the end ofthe demagnetization process of the secondary winding 1114. In anotherexample, the demagnetization detector 1212 outputs a trigger signal 1298to the logic controller 1208 to start a next cycle (e.g., correspondingto a next switching period). In yet another example, when the signal1256 is at a logic high level, the signal 1156 is at a logic high level,and when the signal 1256 is at a logic low level, the signal 1156 is ata logic low level.

In some embodiments, the signal 1236 represents a current and is usedfor adjusting a ramping slope associated with the ramping signal 1228.In certain embodiments, the signal 1238 represents a current and is usedfor adjusting the ramping slope associated with the ramping signal 1228.For example, information associated with both the signal 1236 and thesignal 1238 is used for adjusting the ramping slope associated with theramping signal 1228, so as to adjust the duration of an on-time periodassociated with the drive signal 1156. In another example, the current1236 flows from the current-sensing component 1240 to the ramp-signalgenerator 1202. In yet another example, the current 1236 flows from theramp-signal generator 1202 to the current-sensing component 1240. In yetanother example, the current 1238 flows from thevoltage-to-current-conversion component 1242 to the ramp-signalgenerator 1202. In yet another example, the current 1238 flows from theramp-signal generator 1202 to the voltage-to-current-conversioncomponent 1242.

Referring to FIG. 7(a) and FIG. 7(b), during an on-time period, avoltage 1198 associated with the auxiliary winding 1116 is determined asfollows, in some embodiments:

$\begin{matrix}{V_{aux} = {{- \frac{N_{aux}}{N_{p}}} \times V_{bulk}}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

where V_(aux) represents the voltage 1198, N_(aux)/N_(p) represents aturns ratio between the auxiliary winding 1116 and the primary winding1112, and V_(bulk) represents the bulk voltage 1150. In certainembodiments, when a voltage at the terminal 1140 (e.g., terminal FB) isregulated to be approximately zero, the current signal 1296 is detectedby the current-sensing component 1240:

$\begin{matrix}{I_{FB} = {\frac{V_{aux}}{R_{6}} = {\frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

where I_(FB) represents the current signal 1296 and R₆ represents theresistance of the resistor 1124. According to some embodiments, thecurrent signal 1296 indicates a waveform of the bulk voltage 1150 duringthe on-time period associated with the drive signal 1156, and the signal1236 is determined as follows:

$\begin{matrix}{I_{ac} = {{\delta \times I_{FB}} = {\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}}}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$

where I_(ac) represents the signal 1236 and δ represents a constant.

Similar to what is described above in FIG. 4(c), the ramping signal 1228increases in magnitude during the on-time period, in certainembodiments. For example, the ramping slope of the ramping signal 1228is modulated based on at least information associated with the signal1236 generated through detecting the current signal 1296 during theon-time period. For example, the timing diagram for the controller 1102as part of the system 1100 is similar to what is shown in FIG. 4(c).

FIG. 7(c) is a simplified diagram showing the controller 1102 as part ofthe power conversion system 1100 according to another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecontroller 1102 includes a ramp-signal generator 1602, an under-voltagelock-out (UVLO) component 1604, a modulation component 1606, a logiccontroller 1608, a driving component 1610, a demagnetization detector1612, an error amplifier 1616, a current-sensing component 1614, ajittering-signal generator 1699, and another current-sensing component1640.

In some embodiments, the ramp-signal generator 1602 receives a currentsignal 1694, a jittering signal 1697 (e.g., a jittering current)generated by the jittering-signal generator 1699, and a signal 1636 fromthe current-sensing component 1640 and outputs a ramping signal 1628. Inyet another example, the jittering current 1697 flows from thejittering-signal generator 1699 to the ramp-signal generator 1602. Inyet another example, the jittering current 1697 flows from theramp-signal generator 1602 to the jittering-signal generator 1699. Forexample, a ramping slope associated with the ramping signal 1628 isadjusted based on at least information associated with the signal 1636that is related to a current signal 1696 detected at the terminal 1140(e.g., terminal FB) during an on-time period associated with the drivingsignal 1156. The operations of other components in FIG. 7(c) are similarto what are described in FIG. 7(h). As an example, the signal 1636represents a current. In another example, the current 1636 flows fromthe current-sensing component 1640 to the ramp-signal generator 1602. Inyet another example, the current 1636 flows from the ramp-signalgenerator 1602 to the current-sensing component 1640. In yet anotherexample, the ramping slope of the ramping signal 1628 is modulated inresponse to the jittering signal 1697.

In some embodiments, the jittering signal 1697 corresponds to adeterministic signal, such as a triangle waveform (e.g., with afrequency of several hundred Hz), or a sinusoidal waveform (e.g., with afrequency of several hundred Hz). For example, the jittering signal 1697is associated with multiple jittering cycles corresponding to apredetermined jittering frequency (e.g., approximately constant) relatedto a predetermined jittering period (e.g., approximately constant). Asan example, the signal 1656 is associated with multiple modulationcycles corresponding to a modulation frequency (e.g., not constant)related to a modulation period (e.g., not constant). In another example,the system controller 1102 changes the ramping slope associated with theramping signal 1628 based on at least information associated with thejittering signal 1628 so that, within a same jittering cycle of themultiple jittering cycles, the ramping slope is changed (e.g.,increased, or decreased) by different magnitudes corresponding todifferent modulation cycles respectively. In yet another example, theramping slope is changed during different modulation cycles adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles not adjacent to each other. In yet anotherexample, the system controller 1102 adjusts the modulation frequencybased on at least information associated with the changed ramping slope.

In certain embodiments, the jittering signal 1697 corresponds to arandom (e.g., pseudo-random) signal with a random (e.g., pseudo-random)waveform. For example, the system controller 1102 changes the rampingslope associated with the ramping signal 1628 based on at leastinformation associated with the random jittering signal 1628 so that theramping slope is changed by random magnitudes corresponding to differentmodulation cycles respectively. In yet another example, the rampingslope is changed during different modulation cycles that are adjacent toeach other. In yet another example, the ramping slope is changed duringdifferent modulation cycles that are not adjacent to each other. In yetanother example, the system controller 1102 adjusts the modulationfrequency based on at least information associated with the rampingslope changed by the random magnitudes.

FIG. 8(a) is a simplified diagram showing certain components as part ofthe controller 402 as shown in FIG. 4(b), the controller 802 as shown inFIG. 5(b), and/or the controller 1102 as shown in FIG. 7(b) according tosome embodiments of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. A ramp-signal generator 1300 includes transistors1308, 1310, 1312, 1314, 1316 and 1320, an amplifier 1322, and a NOT gate1324. In addition, current-source components 1302, 1304, 1306 and 1399are included in the controller 402 as shown in FIG. 4(b), the controller802 as shown in FIG. 5(b), and/or the controller 1102 as shown in FIG.7(b).

According to one embodiment, the current-source components 1302, 1304,1306 and 1399 are related to currents 1332, 1334, 1336 and 1397respectively. For example, a current-mirror circuit including thetransistors 1308, 1310, 1312 and 1314 is configured to generate acharging current 1340 (e.g., I_(charge)) that flows through thetransistor 1316 which is controlled by a signal 1328. In anotherexample, the amplifier 1322 receives a reference signal 1330 and outputsan amplified signal 1338. In yet another example, the capacitor 1318 ischarged or discharged to generate a ramping signal 1398 as the outputsignal of the ramp-signal generator 1300.

In some embodiments, the ramp-signal generator 1300 is the same as theramp-signal generator 602, the ramp-signal generator 1002, or theramp-signal generator 1202. For example, the current 1332 is the same asthe current 636 that flows between the ramp-signal generator 602 and thevoltage-to-current-conversion component 640, the current 1036 that flowsbetween the ramp-signal generator 1002 and the current-sensing component1040, or the current 1236 that flows between the ramp-signal generator1202 and the current-sensing component 1240. In another example, thecurrent 1334 is the same as the current 638 that flows between theramp-signal generator 602 and the voltage-to-current-conversioncomponent 642, the current 1038 that flows between the ramp-signalgenerator 1002 and the voltage-to-current-conversion component 1042, orthe current 1238 that flows between the ramp-signal generator 1202 andthe voltage-to-current-conversion component 1242. In yet anotherexample, the current 1336 is the same as the current 694, the current1094, or the current 1294. In yet another example, the current 1397 isthe same as the jittering current 697, the jittering current 1097, orthe jittering current 1297. In yet another example, the ramping signal1398 is the same as the ramping signal 628, the ramping signal 1028, orthe ramping signal 1228. In yet another example, the current-sourcecomponent 1302 is included in the voltage-to-current-conversioncomponent 640, the current-sensing component 1040, or thecurrent-sensing component 1240. In yet another example, thecurrent-source component 1304 is included in thevoltage-to-current-conversion component 642, thevoltage-to-current-conversion component 1042, or thevoltage-to-current-conversion component 1242. In yet another example,the current-source component 1399 is included in the jittering-signalgenerator 699, the jittering-signal generator 1099, or thejittering-signal generator 1299.

In certain embodiments, the ramping slope of the ramping signal 1398 isdetermined as follows:

slope=f(I ₀ , I _(ac) , I _(comp) , I _(j))   (Equation 10)

For example, specifically, the ramping slope of the ramping signal 1398is determined as follows:

slope ∝(α×I ₀ −β×I _(ac) −δ×I _(comp) −γ×I _(j))   (Equation 11A)

where I₀ represents the signal 1336, I_(ac) represents the signal 1332,and I_(comp) represents the signal 1334. In addition, α, β, δ, and γrepresent coefficients (e.g., larger than 0). In another example, theramping slope of the ramping signal 1398 is determined as follows:

slope ∝(α×I ₀ −β×I _(ac) −δ×I _(comp) −γ×I _(j))   (Equation 11B)

In yet another example, the signal 1332 and the signal 1334 aredetermined as follows:

I _(ac) =f1(V _(bulk))

I_(comp) =f2(V _(bulk))   (Equation 12)

where f1 and f2 represent non-linear or linear operators. As an example,

I _(ac)=γ×(V _(bulk) V _(th2)), I _(ac)=0 when V _(bulk) ≦V _(th2)

I _(comp)η×(V _(comp) −V _(th1)), I _(comp)=0 when V _(bulk) ≦V _(th1)  (Equation 13)

where γ and η represent coefficients (e.g., larger than 0), V_(th1) andV_(th2) represent predetermined thresholds.

In one embodiment, if a ratio related to the transistors 1308 and 1310is K and another ratio related to the transistors 1312 and 1314 is M,the charging current 1340 is determined as follows:

I _(charge) =K×M×(I ₀ −I _(ac) −I _(comp) −I _(j))   (Equation 14)

For example, a ramping slope associated with the ramping signal 1398 isdetermined as follows:

$\begin{matrix}{{slope} = \frac{I_{charge}}{C}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

where I_(charge) represents the charging current 1340, and C representsthe capacitance of the capacitor 1318. In certain embodiments, for agiven I₀ and I_(comp), the ramping slope of the ramping signal 1398decreases in magnitude and in turn the duration of an on-time periodincreases when a bulk voltage increases in magnitude. In yet anotherexample, I_(charge) is also determined as follows:

I _(charge) =K×M×(I ₀ −I _(ac) −I _(comp) −I _(j))   (Equation 16)

FIG. 8(b) is a simplified diagram showing certain components as part ofthe controller 402 as shown in FIG. 4(d), the controller 802 as shown inFIG. 5(c), and/or the controller 1102 as shown in FIG. 7(c) according tocertain embodiments of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. A ramp-signal generator 1800 includes transistors1808, 1810, 1812, 1814, 1816 and 1820, an amplifier 1822, and a NOT gate1824. In addition, current-source components 1802, 1806 and 1899 areincluded in the controller 402 as shown in FIG. 4(d), the controller 802as shown in FIG. 5(c), and/or the controller 1102 as shown in FIG. 7(c).

According to one embodiment, the current-source components 1802, 1806and 1899 are related to currents 1832, 1836 and 1897 respectively. Forexample, a current-mirror circuit including the transistors 1808, 1810,1812 and 1814 is configured to generate a charging current 1840 (e.g.,I_(charge)) that flows through the transistor 1816 which is controlledby a signal 1828. In another example, the amplifier 1822 receives areference signal 1830 and outputs an amplified signal 1838. In yetanother example, the capacitor 1818 is charged or discharged to generatea ramping signal 1898 as the output signal of the ramp-signal generator1800.

In some embodiments, the ramp-signal generator 1800 is the same as theramp-signal generator 1402. For example, the current 1832 is the same asthe current 1436 that flows between the ramp-signal generator 1402 andthe voltage-to-current-conversion component 1440, the current 1536 thatflows between the ramp-signal generator 1502 and the current-sensingcomponent 1540, or the current 1636 that flows between the ramp-signalgenerator 1602 and the current-sensing component 1640. In anotherexample, the current 1836 is the same as the current 1494, the current1594, or the current 1694. In yet another example, the current 1897 isthe same as the current 1497, the current 1597, or the current 1697. Inyet another example, the ramping signal 1898 is the same as the rampingsignal 1428, the ramping signal 1528, or the ramping signal 1628. In yetanother example, the current-source component 1802 is included in thevoltage-to-current-conversion component 1440, the current-sensingcomponent 1540, or the current-sensing component 1640. In yet anotherexample, the current-source component 1899 is included in thejittering-signal generator 1499, the jittering-signal generator 1599, orthe jittering-signal generator 1699.

FIG. 8(c) is a simplified diagram showing certain embodiments as part ofthe controller 502 according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. Aramp-signal generator 1700 includes transistors 1708, 1710, 1712, 1714,1716 and 1720, an amplifier 1722, and a NOT gate 1724. In addition,current-source components 1704, 1706 and 1799 are included in thecontroller 502.

According to one embodiment, the current-source components 1704, 1706and 1799 are related to currents 1734, 1736 and 1797 respectively. Forexample, a current-mirror circuit including the transistors 1708, 1710,1712 and 1714 is configured to generate a charging current 1740 (e.g.,I_(charge)) that flows through the transistor 1716 which is controlledby a signal 1728. In another example, the amplifier 1722 receives areference signal 1730 and outputs an amplified signal 1738. In yetanother example, the capacitor 1718 is charged or discharged to generatea ramping signal 1798 as the output signal of the ramp-signal generator1700.

In some embodiments, the ramp-signal generator 1700 is the same as theramp-signal generator 502. For example, the current 1734 is the current738 that flows from the ramp-signal generator 702 to thevoltage-to-current-conversion component 742. In yet another example, thecurrent 1736 is the same as the current 794. In yet another example, thecurrent 1797 is the same as the current 797. In yet another example, theramping signal 1798 is the same as the ramping signal 728. In yetanother example, the current-source component 1704 is included in thevoltage-to-current-conversion component 742. In yet another example, thecurrent-source component 1799 is included in the jittering-signalgenerator 799.

FIG. 9 is a simplified diagram showing certain components of acontroller according to yet another embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. The controller 1900includes voltage-to-current-conversion components 1902 and 1904,current-source components 1906 and 1997, and a ramp-signal generator1999. The ramp-signal generator 1999 includes transistors 1908, 1910,1912, 1914, 1916 and 1920, an amplifier 1922, and a NOT gate 1924. Thevoltage-to-current-conversion component 1902 includes an operationalamplifier 1970, a current-source component 1958, transistors 1960, 1962,1964 and 1968, and a resistor 1966. The voltage-to-current-conversioncomponent 1904 includes an operational amplifier 1976, a current-sourcecomponent 1984, transistors 1978, 1980, 1986 and 1988, and a resistor1982.

According to one embodiment, the voltage-to-current-conversioncomponents 1902 and 1904, the current-source component 1906, and thecurrent-source component 1997 are related to currents 1932, 1934, 1936and 1995 respectively. For example, a current-mirror circuit includingthe transistors 1908, 1910, 1912 and 1914 is configured to generate acharging current 1940 (e.g., I_(charge)) that flows through thetransistor 1916 which is controlled by a signal 1928. In anotherexample, the amplifier 1922 receives a reference signal 1930 and outputsan amplified signal 1938. In yet another example, the capacitor 1918 ischarged or discharged to generate a ramping signal 1998 as the outputsignal of the ramp-signal generator 1999.

According to another embodiment, the operational amplifier 1976 receivesa compensation signal 1974 and outputs a signal 1990 which is receivedby a current-mirror circuit including the transistors 1978, 1980, 1986and 1988 to generate the current 1934. For example, the operationalamplifier 1970 receives a signal 1972 and outputs a signal 1956 which isreceived by a current-mirror circuit including transistors 1968, 1964,1962 and 1960 to generate the current 1932.

In some embodiments, the controller 1900 is the same as the controller402. For example, the ramp-signal generator 1999 is the same as theramp-signal generator 602. As an example, the current 1932 is the sameas the current 636 that flows between the ramp-signal generator 602 andthe voltage-to-current-conversion component 640. In another example, thecurrent 1934 is the same as the current 638 that flows between theramp-signal generator 602 and the voltage-to-current-conversioncomponent 642. In yet another example, the current 1936 is the same asthe current 694. In yet another example, the current 1995 is the same asthe jittering current 697. In yet another example, the ramping signal1998 is the same as the ramping signal 628. In yet another example, thecompensation signal 1974 is related to the compensation signal 474, andthe signal 1972 is related to the signal 472. In yet another example,the voltage-to-current-conversion component 1902 is the same as thevoltage-to-current-conversion component 640. In yet another example, thevoltage-to-current-conversion component 1904 is the same as thevoltage-to-current-conversion component 642. In yet another example, thecurrent-source component 1997 is included in the jittering-signalgenerator 699.

According to another embodiment, based on Equation 12 and Equation 13, acurrent 1992 (e.g., I_(b1) related to the current-source component 1984is associated with η×V_(th1), and a current 1954 (e.g., I_(b2)) relatedto the current-source component 1958 is associated with γ×V_(th2). Forexample, the ramping signal 1998 increases, linearly or non-linearly, toa peak magnitude during each switching period of the power conversionsystem. In another example, a ramping slope associated with the rampingsignal 1998 is determined as follows:

$\begin{matrix}{{slope} = \frac{I_{charge}}{C}} & \left( {{Equation}\mspace{14mu} 16} \right)\end{matrix}$

where I_(charge) represents the charging current 1940, and C representsthe capacitance of the capacitor 1918. In yet another example, anon-time period associated with a drive signal related to a power switchis determined as follows:

$\begin{matrix}{T_{on} = {\frac{V_{comp} - V_{ref}}{I_{charge}} \times C}} & \left( {{Equation}\mspace{14mu} 17} \right)\end{matrix}$

where V_(comp) represents the signal 1974, V_(ref) represents the signal1930, I_(charge) represents the charging current 1940, and C representsthe capacitance of the capacitor 1918.

As discussed above and further emphasized here, FIG. 9 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the current-source component 1904 isremoved from the controller 1900, and the ramp-signal generator 1999 isthen the same as the ramp-signal generator 1800. In another example, thecurrent-source component 1902 is removed from the controller 1900, andthe ramp-signal generator 1999 is then the same as the ramp-signalgenerator 1700.

As discussed above and further emphasized here, FIG. 4(a), FIG. 4(b),FIG. 4(c), and/or FIG. 4(d) are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,to achieve high efficiency (e.g., >90%), the system 400 operates in aquasi-resonant (QR) mode. As an example, the controller 402 isimplemented to change the duration of an on-time period (e.g., T_(on))with the bulk voltage 450 (e.g., associated with a rectified sinewaveform) to improve the total harmonic distortion, e.g., as shown inFIG. 10(a), FIG. 10(b), and/or FIG. 10(c).

FIG. 10(a) is a simplified diagram showing the controller 402 as part ofthe power conversion system 400 according to yet another embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The controller 402 includes a ramp-signal generator 2602, a UVLOcomponent 2604, a modulation component 2606, a logic controller 2608, adriving component 2610, a demagnetization detector 2612, an erroramplifier 2616, a current-sensing-and-sample/hold component 2614, atotal-harmonic-distortion (THD) optimizer 2699, a conversion component2640, and a voltage-to-current-conversion component 2642.

According to one embodiment, the UVLO component 2604 detects the signal454 and outputs a signal 2618 (e.g., por). For example, if the signal454 is larger than a first predetermined threshold in magnitude, thecontroller 402 begins to operate normally. If the signal 454 is smallerthan a second predetermined threshold in magnitude, the controller 402is turned off In another example, the second predetermined threshold issmaller than the first predetermined threshold in magnitude. As anotherexample, the conversion component 2640 receives the signal 472 at theterminal 464 (e.g., terminal VAC) and outputs a signal 2636 to the THDoptimizer 2699. In yet another example, the THD optimizer 2699 alsoreceives the compensation signal 474 at the terminal 448 (e.g., terminalCOMP) and outputs a signal 2697 (e.g., V_(comp) _(_) _(int)). In yetanother example, the THD optimizer 2699 transforms the compensationsignal 474 to the signal 2697 (e.g., V_(comp) _(_) _(int)) based atleast in part on the signal 2636 associated with the signal 472. In yetanother example, the capacitor 434 is coupled to the terminal 448 (e.g.,terminal COMP) and forms, together with the error amplifier 2616, anintegrator or a low-pass filter. In yet another example, the erroramplifier 2616 is a transconductance amplifier and outputs a currentwhich is proportional to a difference between the reference signal 2622and the signal 2620. In yet another example, the error amplifier 2616together with the capacitor 434 generates the compensation signal 474which is a voltage signal. As an example, the signal 2636 includes oneor more current signals. As another example, the signal 2636 includesone or more voltage signals.

According to another embodiment, the error amplifier 2616 receives asignal 2620 from the current-sensing-and-sample/hold component 2614 anda reference signal 2622, and the compensation signal 474 is provided tothe voltage-to-current-conversion component 2642 which outputs a current2638 (e.g., I_(comp)) to the ramp-signal generator 2602. For example,the current-sensing-and-sample/hold component 2614 samples the currentsensing signal 496 in response to the control signal 2630 and then holdsthe sampled signal until the current-sensing-and-sample/hold component2614 samples again the current sensing signal 496. As an example, theramp-signal generator 2602 also receives a current signal 2694 (e.g.,I₀) and generates a ramping signal 2628 to the modulation component 2606(e.g., a comparator) which also receives the signal 2697 (e.g., V_(comp)_(_) _(int)) from the THD optimizer 2699. As an example, the rampingsignal 2628 increases, linearly or non-linearly, to a peak magnitudeduring each switching period. As another example, the ramping slope ofthe ramping signal 2628 varies based at least in part on thecompensation signal 474. In yet another example, the current 2638 (e.g.,I_(comp)) flows from the voltage-to-current-conversion component 2642 tothe ramp-signal generator 2602. In yet another example, the current 2638(e.g., I_(comp)) flows from the ramp-signal generator 2602 to thevoltage-to-current-conversion component 2642.

According to yet another embodiment, the modulation component 2606outputs a modulation signal 2626. For example, the logic controller 2608processes the modulation signal 2626 and outputs a control signal 2630to the current-sensing-and-sample/hold component 2614 and the drivingcomponent 2610. In another example, the driving component 2610 generatesa signal 2656 related to the drive signal 456 to affect the switch 428.In yet another example, if the signal 2656 is at the logic high level,the signal 456 is at the logic high level, and if the signal 2656 is atthe logic low level, the signal 456 is at the logic low level.

In one embodiment, the demagnetization detector 2612 detects thefeedback signal 460 and outputs a demagnetization signal 2632 fordetermining the end of the demagnetization process of the secondarywinding 414. As another example, the demagnetization detector 2612detects the feedback signal 460 and outputs the demagnetization signal2632 for determining the beginning and the end of the demagnetizationprocess of the secondary winding 414. In yet another example, thedemagnetization detector 2612 outputs a trigger signal 2698 to the logiccontroller 2608 to start a next cycle (e.g., corresponding to a nextswitching period).

In another embodiment, the system controller 402 changes the duration ofthe on-time period during which the power switch 428 is kept closed(e.g., being turned on) by different magnitudes corresponding todifferent switching periods of the power switch 428 respectively, basedon at least information associated with the signal 472. For example, theduration of the on-time period associated with the power switch 428 ischanged during different switching periods of the power switch 428adjacent to each other. In another example, the duration of the on-timeperiod associated with the power switch 428 is changed during differentswitching periods of the power switch 428 not adjacent to each other.

FIG. 10(b) is a simplified timing diagram for the controller 402 as partof the power conversion system 400 according to another embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The waveform 2902 represents the signal 2626 as a function of time, thewaveform 2904 represents the signal 2656 as a function of time, the waveform 2906 represents the demagnetization signal 2632 as a function oftime, the waveform 2908 represents the trigger signal 2698 as a functionof time, and the waveform 2910 represents the ramping signal 2628 as afunction of time.

An on-time period and an off-time period associated with the signal 2656are shown in FIG. 10(b). The on-time period begins at a time t₁₃ andends at a time t₁₅, and the off-time period begins at the time t₁₅ andends at a time t₁₈. For example, t₁₀≦t₁₁≦t₁₂≦t₁₃≦t₁₄≦t₁₅≦t₁₆≦t₁₇≦t₁₈.

According to one embodiment, at t₁₀, the demagnetization signal 2632changes from the logic low level to the logic high level. For example,the demagnetization detector 2612 generates a pulse (e.g., between t₁₀and t₁₂) in the trigger signal 2698 to trigger a new cycle. As anexample, the ramping signal 2628 begins to increases from a magnitude2912 to a magnitude 2914 (e.g., at t₁₄). In another example, at t₁₁, thesignal 2626 changes from the logic low level to the logic high level.After a short delay, the signal 2656 changes (e.g., at t₁₃) from thelogic low level to the logic high level, and in response the switch 428is turned on. In yet another example, at t₁₄, the signal 2626 changesfrom the logic high level to the logic low level, and the ramping signal2628 decreases from the magnitude 2914 to the magnitude 2912. After ashort delay, the signal 2656 changes (e.g., at t₁₅) from the logic highlevel to the logic low level, and in response, the switch 428 is turnedoff. As an example, at t₁₆, the demagnetization signal 2632 changes fromthe logic low level to the logic high level which indicates a beginningof a demagnetization process. In another example, at t₁₇, thedemagnetization signal 2632 changes from the logic high level to thelogic low level which indicates an end of the demagnetization process.In yet another example, the demagnetization detector 2612 generatesanother pulse in the trigger signal 2698 to start a next cycle. In yetanother example, the magnitude 2914 of the ramping signal 2628 isassociated with the magnitude of the signal 474.

According to another embodiment, the magnitude change of the rampingsignal 2628 during the on-time period is determined as follows:

ΔV _(ramp) =V _(comp) _(_) _(int) −V _(ref)=slope×T _(on)   (Equation18)

where ΔV_(ramp) represents the magnitude changes of the ramping signal2628, V_(comp) _(_) _(int) represents the signal 2697, V_(ref)represents a predetermined voltage magnitude, slope represents a rampingslope associated with the ramping signal 2628, and T_(on) represents theduration of the on-time period. For example, V_(ref) corresponds to aminimum magnitude of the ramping signal 2628. As an example, based onEquation 18, the duration of the on-time period is determined asfollows:

$\begin{matrix}{T_{on} = \frac{V_{comp\_ int} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 19} \right)\end{matrix}$

According to yet another embodiment, the signal 2697 (e.g., V_(comp)_(_) _(int) is determined as follows:

V _(comp) _(_) _(int) =V _(comp) ÷α×V _(bulk)   (Equation 20)

where V_(comp) represents the compensation signal 474, V_(bulk)represents the bulk voltage 450, and α represents a coefficientparameter. Combining Equations 19 and 20, for example, the duration ofthe on-time period is determined as follows:

$\begin{matrix}{T_{on} = \frac{V_{comp} + {\alpha \times V_{bulk}} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 21} \right)\end{matrix}$

Combining Equations 3 and 21, as an example, the duration of the on-timeperiod is determined as follows:

$\begin{matrix}{T_{on} = \frac{V_{comp} + {\alpha \times {{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}}} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 22} \right)\end{matrix}$

As shown in Equations 21 and 22, the duration of the on-time period isnot constant, and varies with the bulk voltage 450 associated with theAC input signal 452, according to some embodiments. For example,changing the duration of the on-time period with the bulk voltage 450 isapplicable to power conversion systems with a buck-boost topologyoperated in a quasi-resonant (QR) mode. In another example, a slope ofthe waveform 2910 between t₁₁ and t₁₄ corresponds to the ramping slopeof the ramping signal 2628. In yet another example, changing theduration of the on-time period with the bulk voltage 450 is applicableto power conversion systems with a flyback topology operated in aquasi-resonant (QR) mode.

FIG. 10(c) is a simplified diagram showing certain components of thecontroller 402 as part of the system 400 according to another embodimentof the present invention. This diagram is merely an example, whichshould not unduly limit the scope of the claims. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications.

For example, the voltage-to-current-conversion component 2642 includesan operational amplifier 3976, a current-source component 3984,transistors 3978, 3980, 3986 and 3988, and a resistor 3982. Theramp-signal generator 2602 includes transistors 3908, 3910, 3912, 3914,3916 and 3920, an amplifier 3922, and an NOT gate 3924. The conversioncomponent 2640 includes an operational amplifier 3970, a current-sourcecomponent 3958, transistors 3995, 3997, 3932, 3960, 3962, 3964 and 3968,and a resistor 3966. The THD optimizer 2699 includes an operationalamplifier 3936, and resistors 3944 and 3946. The controller 402 furtherincludes a current-source component 3906 which provides the currentsignal 2694 (e.g., I₀). As an example, the transistors 3908, 3910, 3920,3986, 3988, 3962, 3960 and 3932 are N-channel transistors, and thetransistors 3978, 3980, 3912, 3914, 3916, 3968, 3964, 3995 and 3997 areP-channel transistors.

According to one embodiment, the amplifier 3922 receives a referencesignal 3930 (e.g., V_(ref)) at its non-inverting terminal (e.g.,terminal “+”) and outputs an amplified signal 3938, where the invertingterminal (e.g., terminal “−”) and the output terminal of the amplifier3922 are connected together. For example, the signal 3928 (e.g., PWM_N)is generated by the NOT gate 3924 and is complementary to the modulationsignal 2626 (e.g., PWM). As an example, if the modulation signal 2626(e.g., PWM) is at the logic high level, the signal 3928 (e.g., PWM_N) isat the logic low level, and if the modulation signal 2626 (e.g., PWM) isat the logic low level, the signal 3928 (e.g., PWM_N) is at the logichigh level. In another example, the transistors 3920 and the transistor3916 are controlled by the signal 3928 (e.g., PWM_N). In one embodiment,if the signal 3928 (e.g., PWM_N) is at the logic high level, thetransistor 3920 is turned on and the transistor 3916 is turned off. Theamplified signal 3938 is provided through the transistor 3920 togenerate the ramping signal 2628 as the output signal of the ramp-signalgenerator 2602. In another embodiment, if the signal 3928 (e.g., PWM_N)is at the logic low level, the transistor 3920 is turned off and thetransistor 3916 is turned on. A current-mirror circuit including thetransistors 3908, 3910, 3912 and 3914 is configured to generate acharging current 3940 (e.g., I_(charge)) that flows through thetransistor 3916. The capacitor 3918 is charged in response to thecurrent 3940 through the transistor 3916 to generate the ramping signal2628 as the output signal of the ramp-signal generator 2602.

According to another embodiment, the operational amplifier 3976 receivesthe compensation signal 474 (e.g., V_(comp)) at its non-invertingterminal (e.g., terminal “+”) and outputs a signal 3990 which isreceived by a current-mirror circuit including the transistors 3978,3980, 3986 and 3988 to generate the current 2638 (e.g., I_(comp)). Forexample, a current 3981 that flows through the transistor 3978 isproportional in magnitude to (e.g., equal to) a sum of a current 3992provided by the current-source component 3984 and a current 3991 thatflows through the transistor 3986. In another example, the current 3991is proportional in magnitude to (e.g., equal to) the current 2638 (e.g.,I_(comp)). In yet another example, the current 2694 (e.g., I₀) isproportional in magnitude to (e.g., equal to) a sum of the current 2638(e.g., I_(comp)) and a current 3911 that flows through the transistor3908. In yet another example, the current 3911 is proportional inmagnitude to (e.g., equal to) the current 3940 (e.g., I_(charge)).

According to yet another embodiment, the operational amplifier 3970receives the signal 472 associated with the bulk voltage 450 and outputsa signal 3956 to the transistor 3968 to generate a current 3967 flowingthrough the resistor 3966 (e.g., R2). For example, a current-mirrorcircuit including the transistors 3968 and 3964 generates a current 3969that flows through the transistor 3964. As an example, the current 3969is proportional in magnitude to (e.g., equal to) the current 3967. Asanother example, the current-source component 3958 provides a current3954 (e.g., Ib2), and a current 3963 that flows through the transistor3962 is equal in magnitude to a difference between the current 3969 andthe current 3954. As yet another example, a current-mirror circuitincluding the transistors 3962 and 3960 generates a current 3961. Forexample, the current 3961 flows through the transistor 3960 and ismirrored to generate a current 3942 (e.g., I_(ac) _(_) _(n)). In anotherexample, the current 3961 flows through the transistor 3995 and ismirrored to generate a current 3940 (e.g., I_(ac) _(_) _(p)). In yetanother example, the current 3961 is proportional in magnitude to (e.g.,equal to) the current 3940 (e.g., I_(ac) _(_) _(p)). In yet anotherexample, the current 3961 is proportional in magnitude to (e.g., equalto) the current 3942 (e.g., I_(ac) _(_) _(n)).

In one embodiment, the THD optimizer 2699 receives both the current 3940(e.g., I_(ac) _(_) _(p)) and the current 3942 (e.g., I_(ac) _(_) _(n))as well as the compensation signal 474 (e.g., V_(comp)) and outputs thesignal 2697 (e.g., I_(comp) _(_) _(int)) to the modulation component2606 (e.g., a comparator). As an example, the operational amplifier 3936receives the compensation signal 474 (e.g., V_(comp)) at itsnon-inverting terminal (e.g., terminal “+”), where the invertingterminal (e.g., terminal “−”) and the output terminal of the amplifier3936 are connected together. As another example, the current 3942 (e.g.,I_(ac) _(_) _(n)) flows through the resistor 3944 (e.g., R3) and thecurrent 3940 (e.g., I_(ac) _(_) _(p)) flows through the resistor 3946(e.g., R4) to generate the signal 2697 (e.g., V_(comp) _(_) _(int)). Forexample, the current 3940 (e.g., I_(ac) _(_) _(p)) and the current 3942(e.g., I_(ac) _(_) _(n)) are included in the signal 2636 generated bythe conversion component 2640 (e.g., as shown in FIG. 10(a)).

In another embodiment, the current 3940 (e.g., I_(ac) _(_) _(p)) isdetermined as follows:

$\begin{matrix}{I_{ac\_ p} = {\frac{VAC}{R\; 2} - {{Ib}\; 2}}} & \left( {{Equation}\mspace{14mu} 23} \right)\end{matrix}$

where VAC represents the signal 472, R2 represents the resistance of theresistor 3966, and Ib2 represents the current 3954. As an example,VAC=γ×V_(bulk), where γ represents a coefficient parameter. For example,

${{\gamma \times \frac{V_{bulk}}{R\; 2}} \geq {{Ib}\; 2}},$

if the current 3940 (e.g., I_(ac) _(_) _(p)) is determined as follows:

$\begin{matrix}{I_{ac\_ p} = {\frac{\gamma \times V_{bulk}}{R\; 2} - {{Ib}\; 2}}} & \left( {{Equation}\mspace{14mu} 24} \right)\end{matrix}$

In another example, if

${{\gamma \times \frac{V_{bulk}}{R\; 2}} < {{Ib}\; 2}},$

the current 3940 (e.g., I_(ac) _(_) _(p)) is determined to be zero. Insome embodiments, the current 3942 (e.g., I_(ac) _(_) _(n)) is equal inmagnitude to the current 3940 (e.g., I_(ac) _(_) _(p)).

In yet another embodiment, if

${{{\gamma \times \frac{V_{bulk}}{R\; 2}} - {{Ib}\; 2}} \geq 0},$

the signal 2697 (e.g., V_(comp) _(_) _(int)) is determined as follows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\left( {\frac{\gamma \times V_{bulk}}{R\; 2} - {{Ib}\; 2}} \right) \times R\; 3}}}\end{matrix} & \left( {{Equation}\mspace{14mu} 25} \right)\end{matrix}$

where V_(comp) represents the compensation signal 474, R3 represents theresistance of the resistor 3944, and R4 represents the resistance of theresistor 3946. For example, if Ib2 is equal to zero, the signal 2697(e.g., V_(comp) _(_) _(int)) is determined, based on Equation 25, asfollows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\frac{\gamma \times V_{bulk}}{R\; 2} \times R\; 3}}}\end{matrix} & \left( {{Equation}\mspace{14mu} 26} \right)\end{matrix}$

Combining Equation 3 and Equation 26, the signal 2697 (e.g., V_(comp)_(_) _(int)) is determined as follows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\frac{\gamma \times {{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}}}{R\; 2} \times R\; 3}}}\end{matrix} & \left( {{Equation}\mspace{14mu} 27} \right)\end{matrix}$

In yet another embodiment, combining Equation 19 and Equation 27, theduration of the on-time period associated with the switch 428 isdetermined as follows:

$\begin{matrix}{T_{on} = \frac{{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\frac{\gamma \times {{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}}}{R\; 2} \times R\; 3} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 28} \right)\end{matrix}$

As discussed above and further emphasized here, FIG. 5(a), FIG. 5(b),and/or FIG. 5(c) are merely examples, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, toachieve high efficiency (e.g., >90%), the system 800 operates in aquasi-resonant (QR) mode. As an example, the controller 802 isimplemented to change the duration of an on-time period (e.g., T_(on))with the bulk voltage 850 (e.g., associated with a rectified sinewaveform) to improve the total harmonic distortion, e.g., as shown inFIG. 11(a) and/or FIG. 11(b).

FIG. 11(a) is a simplified diagram showing the controller 802 as part ofthe power conversion system 800 according to yet another embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The controller 802 includes a ramp-signal generator 3002, a UVLOcomponent 3004, a modulation component 3006, a logic controller 3008, adriving component 3010, a demagnetization detector 3012, an erroramplifier 3016, a current-sensing-and-sample/hold component 3014, atotal-harmonic-distortion (THD) optimizer 3099, a current-sensingcomponent 3040, and a voltage-to-current-conversion component 3042.

According to one embodiment, the UVLO component 3004 detects the signal854 and outputs a signal 3018 (e.g., por). For example, if the signal854 is larger than a first predetermined threshold in magnitude, thecontroller 802 begins to operate normally. If the signal 854 is smallerthan a second predetermined threshold in magnitude, the controller 802is turned off. In another example, the second predetermined threshold issmaller than the first predetermined threshold in magnitude. As anotherexample, the current-sensing component 3040 receives the signal 872 atthe terminal 864 (e.g., terminal I_AC) and outputs a signal 3036 to theTHD optimizer 3099. In yet another example, the THD optimizer 3099 alsoreceives the compensation signal 874 at the terminal 848 (e.g., terminalCOMP) and outputs a signal 3097 (e.g., V_(comp) _(_) _(int)). In yetanother example, the THD optimizer 3099 transforms the compensationsignal 874 to the signal 3097 (e.g., V_(comp) _(_) _(int)) based atleast in part on the signal 3036 associated with the signal 872. In yetanother example, the capacitor 834 is coupled to the terminal 848 (e.g.,terminal COMP) and forms, together with the error amplifier 3016, anintegrator or a low-pass filter. In yet another example, the erroramplifier 3016 is a transconductance amplifier and outputs a currentwhich is proportional to a difference between the reference signal 3022and the signal 3020. In yet another example, the error amplifier 3016together with the capacitor 834 generates the compensation signal 874which is a voltage signal. As an example, the signal 3036 includes oneor more current signals. As another example, the signal 3036 includesone or more voltage signals.

According to another embodiment, the error amplifier 3016 receives asignal 3020 from the current-sensing-and-sample/hold component 3014 anda reference signal 3022, and the compensation signal 874 is alsoprovided to the voltage-to-current-conversion component 3042 whichoutputs a current 3038 (e.g., I_(comp)) to the ramp-signal generator3002. For example, the current-sensing-and-sample/hold component 3014samples the current sensing signal 896 in response to the control signal3030 and then holds the sampled signal until thecurrent-sensing-and-sample/hold component 3014 samples again the currentsensing signal 896. As an example, the ramp-signal generator 3002 alsoreceives a current signal 3094 (e.g., I₀) and generates a ramping signal3028 to the modulation component 3006 (e.g., a comparator) which alsoreceives the signal 3097 (e.g., V_(comp) _(_) _(int)) from the THDoptimizer 3099. As an example, the ramping signal 3028 increases,linearly or non-linearly, to a peak magnitude during each switchingperiod. As another example, the ramping slope of the ramping signal 3028varies based at least in part on the compensation signal 874. In yetanother example, the current 3038 (e.g., I_(comp)) flows from thevoltage-to-current-conversion component 3042 to the ramp-signalgenerator 3002. In yet another example, the current 3038 (e.g.,I_(comp)) flows from the ramp-signal generator 3002 to thevoltage-to-current-conversion component 3042.

According to yet another embodiment, the modulation component 3006outputs a modulation signal 3026. For example, the logic controller 3008processes the modulation signal 3026 and outputs a control signal 3030to the current-sensing-and-sample/hold component 3014 and the drivingcomponent 3010. In another example, the driving component 3010 generatesa signal 3056 related to the drive signal 856 to affect the switch 828.In another example, if the signal 3056 is at a logic high level, thesignal 856 is at a logic high level, and if the signal 3056 is at alogic low level, the signal 856 is at a logic low level.

In one embodiment, the demagnetization detector 3012 detects thefeedback signal 860 and outputs a demagnetization signal 3032 fordetermining the end of the demagnetization process of the secondarywinding 814. As another example, the demagnetization detector 3012detects the feedback signal 860 and outputs the demagnetization signal3032 for determining the beginning and the end of the demagnetizationprocess of the secondary winding 814. In yet another example, thedemagnetization detector 3012 outputs a trigger signal 3098 to the logiccontroller 3008 to start a next cycle (e.g., corresponding to a nextswitching period).

In another embodiment, the system controller 802 changes the duration ofthe on-time period during which the power witch 828 is kept closed(e.g., being turned on) by different magnitudes corresponding todifferent switching periods of the power switch 828 respectively, basedon at least information associated with the signal 872. For example, theduration of the on-time period associated with the power switch 828 ischanged during different switching periods of the power switch 828adjacent to each other. In another example, the duration of the on-timeperiod associated with the power switch 828 is changed during differentswitching periods of the power switch 828 not adjacent to each other.

FIG. 11(b) is a simplified diagram showing certain components of thecontroller 802 as part of the system 800 according to one embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.

For example, the ramp-signal generator 3002 includes transistors 3108,3110, 3112, 3114, 3116 and 3120, an amplifier 3122, and an NOT gate3124. The THD optimizer 3099 includes an operational amplifier 3136, andresistors 3144 and 3146. The current-sensing component 3040 includestransistors 3132, 3160, 3162, 3164 and 3168, and a current-sourcecomponent 3134. As an example, the transistors 3108, 3110, 3120, 3162,3160 and 3132 are N-channel transistors, and the transistors 3112, 3114,3116, 3168 and 3164 are P-channel transistors.

According to one embodiment, the amplifier 3122 receives a referencesignal 3130 (e.g., V_(ref)) at its non-inverting terminal (e.g.,terminal “+”) and outputs an amplified signal 3138, where the invertingterminal (e.g., terminal “−”) and the output terminal of the amplifier3122 are connected together. In another example, the signal 3128 (e.g.,PWM_N) is generated by the NOT gate 3124 and is complementary to themodulation signal 3026 (e.g., PWM). As an example, if the modulationsignal 3026 (e.g., PWM) is at the logic high level, the signal 3128(e.g., PWM_N) is at the logic low level, and if the modulation signal3026 (e.g., PWM) is at the logic low level, the signal 3128 (e.g.,PWM_N) is at the logic high level. In another example, the transistors3120 and the transistor 3116 are controlled by the signal 3128 (e.g.,PWM_N). In one embodiment, if the signal 3128 (e.g., PWM_N) is at thelogic high level, the transistor 3120 is turned on and the transistor3116 is turned off. The amplified signal 3138 is provided through thetransistor 3120 to generate the ramping signal 3028 as the output signalof the ramp-signal generator 3002. In another embodiment, if the signal3128 (e.g., PWM_N) is at the logic low level, the transistor 3120 isturned off and the transistor 3116 is turned on. A current-mirrorcircuit including the transistors 3108, 3110, 3112 and 3114 isconfigured to generate a charging current 3140 (e.g., I_(charge)) thatflows through the transistor 3116. The capacitor 3118 is charged inresponse to the current 3140 through the transistor 3116 to generate theramping signal 3028 as the output signal of the ramp-signal generator3002. For example, a current 3198 flows through the transistor 3108 andis proportional in magnitude to the current 3140 (e.g., I_(charge)). Inanother example, the current 3094 (e.g., I₀) is equal in magnitude to asum of the current 3198 and the current 3038 (e.g., I_(comp)).

According to another embodiment, a current 3196 flows through thetransistor 3162 and the current 872 (e.g., I_(ac)) is equal in magnitudeto a sum of the current 3196 and a current 3154 (e.g., Ib2) provided bythe current-source component 3134. For example, a current-mirror circuitincluding the transistors 3162, 3160 and 3132 generates a current 3142(e.g., I_(ac) _(_) _(n)) which is proportional in magnitude to (e.g.,equal to) the current 3196. In another example, a current-mirror circuitincluding the transistors 3162, 3160, 3168 and 3164 generates a current3140 (e.g., I_(ac) _(_) _(p)) which is proportional in magnitude to(e.g., equal to) the current 3196.

According to yet another embodiment, the operational amplifier 3136receives the compensation signal 874 (e.g., V_(comp)) at itsnon-inverting terminal (e.g., terminal “+”) and outputs a signal 3190 tothe resistor 3144 (e.g., R3) and the resistor 3146 (e.g., R4). Forexample, the signal 3190 is associated with at least the current 3142(I_(ac) _(_) _(n)). As an example, the signal 3097 (e.g., V_(comp) _(_)_(int)) is generated based at least in part on the current 3140 (e.g.,I_(ac) _(_) _(p)) and the current 3142 (I_(ac) _(_) _(n)) and output tothe modulation component 3006 (e.g., a comparator). For example, thecurrent 3140 (e.g., I_(ac) _(_) _(p)) and the current 3142 (e.g., I_(ac)_(_) _(n)) are included in the signal 3036 generated by thecurrent-sensing component 3040 (e.g., as shown in FIG. 11(a)).

In one embodiment, if I_(ac)≧Ib2, the current 3140 (e.g., I_(ac) _(_)_(p)) is determined as follows:

I _(ac) _(_) _(p) =I _(ac) −Ib2   (Equation 29)

where I_(ac) represents the current signal 872, and Ib2 represents thecurrent 3154. For example, if I_(ac)<Ib2, the current 3140 (e.g., I_(ac)_(_) _(p)) is determined to be zero. In some embodiments, the current3142 (e.g., I_(ac) _(_) _(n)) is equal in magnitude to the current 3140(e.g., I_(ac) _(_) _(p)).

As discussed above and further emphasized here, FIG. 7(a), FIG. 7(b),and/or FIG. 7(c) are merely examples, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, toachieve high efficiency (e.g., >90%), the system 1100 operates in aquasi-resonant (QR) mode. As an example, the controller 1102 isimplemented to change the duration of an on-time period (e.g., T_(on))with the bulk voltage 1150 (e.g., associated with a rectified sinewaveform) to improve the total harmonic distortion, e.g., as shown inFIG. 12(a) and/or FIG. 12(b).

FIG. 12(a) is a simplified diagram showing the controller 1102 as partof the power conversion system 1100 according to another embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The controller 1102 includes a ramp-signal generator 3202, a UVLOcomponent 3204, a modulation component 3206, a logic controller 3208, adriving component 3210, a demagnetization detector 3212, an erroramplifier 3216, a current-sensing-and-sample/hold component 3214, acurrent-sensing component 3240, a total-harmonic-distortion (THD)optimizer 3299, and a voltage-to-current-conversion component 3242.

According to one embodiment, the UVLO component 3204 detects the signal1154 and outputs a signal 3218 (e.g., por). For example, if the signal1154 is larger than a first predetermined threshold in magnitude, thecontroller 1102 begins to operate normally. If the signal 1154 issmaller than a second predetermined threshold in magnitude, thecontroller 1102 is turned off In another example, the firstpredetermined threshold is larger than the second predeterminedthreshold in magnitude.

According to another embodiment, the ramp-signal generator 3202 receivesa current signal 3294 (e.g., I₀) and a current 3238 (e.g., I_(comp))from the voltage-to-current-conversion component 3242 and generates aramping signal 3228 to the modulation component 3206. As an example, theramping signal 3228 increases, linearly or non-linearly, to a peakmagnitude during each switching period. As another example, the rampingslope of the ramping signal 3228 varies based at least in part on thecompensation signal 1174. In another example, the modulation component3206 also receives a signal 3297 (e.g., V_(comp) _(_) _(in)) from theTHD optimizer 3299 and outputs a modulation signal 3226 to the logiccontroller 3208. For example, the logic controller 3208 processes themodulation signal 3226 and outputs a control signal 3230 to thecurrent-sensing-and-sample/hold component 3214 and the driving component3210. In another example, the driving component 3210 generates a signal3256 related to the drive signal 1156 to affect the switch 1128. In yetanother example, if the signal 3256 is at the logic high level, thesignal 1156 is at the logic high level, and if the signal 3256 is at thelogic low level, the signal 1156 is at the logic low level.

According to yet another embodiment, the error amplifier 3216 receives asignal 3220 from the current-sensing-and-sample/hold component 3214 anda reference signal 3222 (e.g., V_(ref) _(_) _(ea)) and the compensationsignal 1174 is provided to the THD optimizer 3299 and thevoltage-to-current-conversion component 3242. As an example, thecapacitor 1134 is coupled to the terminal 1148 (e.g., terminal COMP) andforms, together with the error amplifier 3216, an integrator or alow-pass filter. In another example, the error amplifier 3216 is atransconductance amplifier and outputs a current which is proportionalto a difference between the reference signal 3222 and the signal 3220.In yet another example, the error amplifier 3216 together with thecapacitor 1134 generates the compensation signal 1174 which is a voltagesignal. In yet another example, the current 3238 (e.g., I_(comp)) flowsfrom the THD optimizer 3299 to the ramp-signal generator 3202. In yetanother example, the current 3238 (e.g., I_(comp)) flows from theramp-signal generator 3202 to the THD optimizer 3299.

According to yet another embodiment, the current-sensing component 3240outputs a signal 3236 to the ramp-signal generator 3202 in response to acurrent signal 3296 associated with the terminal 1140 (e.g., terminalFB). For example, the current signal 3296 is related to the bulk voltage1150 during the on-time period associated with the driving signal 1156.As an example, the signal 3236 includes one or more current signals. Asanother example, the signal 3236 includes one or more voltage signals.

In one embodiment, the demagnetization detector 3212 detects thefeedback signal 1160 and outputs a demagnetization signal 3232 fordetermining the end of the demagnetization process of the secondarywinding 1114. As another example, the demagnetization detector 3212detects the feedback signal 1160 and outputs the demagnetization signal3232 for determining the beginning and the end of the demagnetizationprocess of the secondary winding 1114. In yet another example, thedemagnetization detector 3212 outputs a trigger signal 3298 to the logiccontroller 3208 to start a next cycle (e.g., corresponding to a nextswitching period).

In another embodiment, the system controller 1102 changes the durationof the on-time period during which the power witch 1128 is kept closed(e.g., being turned on) by different magnitudes corresponding todifferent switching periods of the power switch 1128 respectively. Forexample, the duration of the on-time period associated with the powerswitch 1128 is changed during different switching periods of the powerswitch 1128 adjacent to each other. In another example, the duration ofthe on-time period associated with the power switch 1128 is changedduring different switching periods of the power switch 1128 not adjacentto each other.

FIG. 12(b) is a simplified diagram showing certain components of thecontroller 1102 as part of the system 1100 according to one embodimentof the present invention. This diagram is merely an example, whichshould not unduly limit the scope of the claims. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications.

For example, the ramp-signal generator 3202 includes transistors 3308,3310, 3312, 3314, 3316 and 3320, an amplifier 3322, and an NOT gate3324. The THD optimizer 3299 includes an operational amplifier 3336, andresistors 3344 and 3346. The current-sensing component 3240 includestransistors 3332, 3360, 3362, 3364 and 3368, and a current-sourcecomponent 3334. As an example, the transistors 3308, 3310, 3320, 3362,3360 and 3332 are N-channel transistors, and the transistors 3312, 3314,3316, 3368 and 3364 are P-channel transistors.

According to one embodiment, the amplifier 3322 receives a referencesignal 3330 (e.g., V_(ref)) at its non-inverting terminal (e.g.,terminal “+”) and outputs an amplified signal 3338, where the invertingterminal (e.g., terminal “−”) and the output terminal of the amplifier3322 are connected together. For example, the signal 3328 (e.g., PWM_N)is generated by the NOT gate 3324 and is complementary to the modulationsignal 3226 (e.g., PWM). As an example, if the modulation signal 3226(e.g., PWM) is at the logic high level, the signal 3328 (e.g., PWM_N) isat the logic low level, and if the modulation signal 3226 (e.g., PWM) isat the logic low level, the signal 3328 (e.g., PWM_N) is at the logichigh level. In another example, the transistors 3320 and the transistor3316 are controlled by the signal 3328 (e.g., PWM_N). In one embodiment,if the signal 3328 (e.g., PWM_N) is at the logic high level, thetransistor 3320 is turned on and the transistor 3316 is turned off Theamplified signal 3338 is provided through the transistor 3320 togenerate the ramping signal 3228 as the output signal of the ramp-signalgenerator 3202. In another embodiment, if the signal 3328 (e.g., PWM_N)is at the logic low level, the transistor 3320 is turned off and thetransistor 3316 is turned on. A current-mirror circuit including thetransistors 3308, 3310, 3312 and 3314 is configured to generate acharging current 3340 (e.g., I_(charge)) that flows through thetransistor 3316. The capacitor 3318 is charged in response to thecurrent 3340 through the transistor 3316 to generate the ramping signal3228 as the output signal of the ramp-signal generator 3202. Forexample, a current 3398 flows through the transistor 3308 and isproportional in magnitude to the current 3340 (e.g., I_(charge)). Inanother example, the current 3294 (e.g., I₀) is equal in magnitude to asum of the current 3398 and the current 3238 (e.g., I_(comp)).

According to another embodiment, a current 3396 flows through thetransistor 3362, and a current 3496 (e.g., I_(ac)) associated with thecurrent 3296 (e.g., I_(FB)) is equal in magnitude to a sum of thecurrent 3396 and a current 3354 (e.g., Ib2) provided by thecurrent-source component 3334. For example, a current-minor circuitincluding the transistors 3362, 3360 and 3332 generates a current 3342(e.g., I_(ac) _(_) _(n)) which is proportional in magnitude to (e.g.,equal to) the current 3396. In another example, a current-mirror circuitincluding the transistors 3362, 3360, 3368 and 3364 generates a current3340 (e.g., I_(ac) _(_) _(p)) which is proportional in magnitude to(e.g., equal to) the current 3396.

According to yet another embodiment, the operational amplifier 3336receives the compensation signal 1174 (e.g., V_(comp)) at itsnon-inverting terminal (e.g., terminal “+”) and outputs a signal 3390 tothe resistor 3344 (e.g., R3) and the resistor 3346 (e.g., R4). Forexample, the signal 3390 is associated with at least the current 3342(I_(ac) _(_) _(n)). As an example, the signal 3297 (e.g., V_(comp) _(_)_(int)) is generated based at least in part on the current 3340 (e.g.,I_(ac) _(_) _(p)) and the current 3342 (I_(ac) _(_) _(n)) and output tothe modulation component 3206 (e.g., a comparator). For example, thecurrent 3340 (e.g., I_(ac) _(_) _(p)) and the current 3342 (e.g., I_(ac)_(_) _(n)) are included in the signal 3236 generated by thecurrent-sensing component 3240 (e.g., as shown in FIG. 12(a)).

Referring to FIG. 7(a), FIG. 12(a) and FIG. 12(b), during an on-timeperiod, the voltage 1198 associated with the auxiliary winding 1116 isdetermined as follows, in some embodiments:

$\begin{matrix}{V_{aux} = {\frac{N_{aux}}{N_{p}} \times V_{bulk}}} & \left( {{Equation}\mspace{14mu} 30} \right)\end{matrix}$

where V_(aux) represents the voltage 1198, N_(aux)/N_(p) represents aturns ratio between the auxiliary winding 1116 and the primary winding1112, and V_(bulk) represents the bulk voltage 1150. In certainembodiments, if a voltage at the terminal 1140 (e.g., terminal FB) isregulated to be approximately zero, the current signal 3296 (e.g.,I_(FB)) is detected by the current-sensing component 3240:

$\begin{matrix}{I_{FB} = {\frac{V_{aux}}{R_{6}} = {\frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}}}} & \left( {{Equation}\mspace{14mu} 31} \right)\end{matrix}$

where I_(FB) represents the current signal 3296 and R₆ represents theresistance of the resistor 1124.

According to some embodiments, the current signal 3296 indicates awaveform of the bulk voltage 1150 during the on-time period associatedwith the drive signal 1156, and the current signal 3496 is determined asfollows:

$\begin{matrix}{I_{ac} = {{\delta \times I_{FB}} = {\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}}}} & \left( {{Equation}\mspace{14mu} 32} \right)\end{matrix}$

where I_(ac) represents the current signal 3496 and δ represents aconstant. For example, if I_(ac)≧Ib2, the current 3340 (e.g., I_(ac)_(_) _(p)) is determined as follows:

I _(ac) _(_) _(p) =I _(ac) −Ib2   (Equation 33)

where I_(ac) represents the current signal 3496, and Ib2 represents thecurrent 3354. For example, if I_(ac)<Ib2, the current 3340 (e.g., I_(ac)_(_) _(p)) is determined to be zero. In some embodiments, the current3342 (e.g., I_(ac) _(_) _(n)) is equal in magnitude to the current 3340(e.g., I_(ac) _(_) _(p)).

In one embodiment, if

${{{\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}} - {{Ib}\; 2}} \geq 0},$

the signal 3297 (e.g., V_(comp) _(_) _(int)) is determined as follows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} +}} \\{{\left( {{\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk}} - {{Ib}\; 2}} \right) \times R\; 3}}\end{matrix} & \left( {{Equation}\mspace{14mu} 34} \right)\end{matrix}$

where V_(comp) represents the compensation signal 1174, R3 representsthe resistance of the resistor 3344, and R4 represents the resistance ofthe resistor 3346. For example, if Ib2 is equal to zero, the signal 3297(e.g., V_(comp) _(_) _(int)) is determined, based on Equation 34, asfollows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times V_{bulk} \times R\; 3}}}\end{matrix} & \left( {{Equation}\mspace{14mu} 35} \right)\end{matrix}$

Combining Equation 3 and Equation 35, the signal 3297 (e.g., V_(comp)_(_) _(int)) is determined as follows:

$\begin{matrix}\begin{matrix}{V_{comp\_ int} = {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {I_{ac\_ p} \times R\; 3}}} \\{= {{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times}}} \\{{{{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}} \times R\; 3}}\end{matrix} & \left( {{Equation}\mspace{14mu} 36} \right)\end{matrix}$

In another embodiment, the magnitude change of the ramping signal 3228during the on-time period is determined as follows:

ΔV _(ramp) =V _(comp) _(_) _(int) −V _(ref)=slope×T _(on)   (Equation37)

where ΔV_(ramp) represents the magnitude changes of the ramping signal3228, V_(comp) _(_) _(int) represents the signal 3297, V_(ref)represents a predetermined voltage magnitude (e.g., the signal 3330),slope represents a ramping slope associated with the ramping signal3228, and T_(on) represents the duration of the on-time period. Forexample, V_(ref) corresponds to a minimum magnitude of the rampingsignal 3228. As an example, based on Equation 37, the duration of theon-time period is determined as follows:

$\begin{matrix}{T_{on} = \frac{V_{{comp\_ in}t} - V_{ref}}{slope}} & \left( {{Equation}\mspace{14mu} 38} \right)\end{matrix}$

Based on Equation 36 and Equation 38, the duration of the on-time periodis determined as follows:

$\begin{matrix}{T_{on} = \frac{\begin{matrix}{{\frac{R\; 4}{{R\; 3} + {R\; 4}} \times V_{comp}} + {\delta \times \frac{N_{aux}}{N_{p} \times R_{6}} \times}} \\{{{{A\; {\sin \left( {{\omega \; t} + \phi} \right)}}} \times R\; 3} - V_{ref}}\end{matrix}}{slope}} & \left( {{Equation}\mspace{14mu} 39} \right)\end{matrix}$

According to one embodiment, a system controller for regulating a powerconversion system includes a first controller terminal and a secondcontroller terminal. The first controller terminal is configured toreceive a first signal associated with an input signal for a primarywinding of a power conversation system. The second controller terminalis configured to output a drive signal to a switch to affect a firstcurrent flowing through the primary winding of the power conversionsystem, the drive signal being associated with an on-time period, theswitch being closed during the on-time period. The system controller isconfigured to adjust a duration of the on-time period based on at leastinformation associated with the first signal. For example, the systemcontroller is implemented according to at least FIG. 4(a), FIG. 4(b),FIG. 4(d), FIG. 5(a), FIG. 5(b), FIG. 5(c), FIG. 7(a), FIG. 7(b), FIG.7(c), FIG. 8(a), FIG. 8(b), and/or FIG. 9.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal, aramp-signal generator, and a second controller terminal. The firstcontroller terminal is configured to provide a compensation signal basedon at least information associated with a first current flowing througha primary winding of a power conversion system. The ramp-signalgenerator is configured to receive a first signal associated with thecompensation signal and generate a ramping signal based on at leastinformation associated with the first signal, the ramping signal beingassociated with a ramping slope. The second controller terminal isconfigured to output a drive signal to a switch based on at leastinformation associated with the ramping signal to affect the firstcurrent. The system controller is configured to adjust the ramping slopeof the ramping signal based on at least information associated with thecompensation signal. For example, the system controller is implementedaccording to at least FIG. 4(a), FIG. 4(b), FIG. 5(a), FIG. 5(b), FIG.6(a), FIG. 6(b), FIG. 7(a), FIG. 7(b), FIG. 8(a), FIG. 8(c), and/or FIG.9.

According to yet another embodiment, a method for regulating a powerconversion system includes: receiving a first signal from a firstcontroller terminal, the first signal being associated with an inputsignal for a primary winding of a power conversation system; adjusting aduration of an on-time period related to a drive signal based on atleast information associated with the first signal; and outputting thedrive signal from a second controller terminal to a switch to affect afirst current flowing through the primary winding of the powerconversion system, the switch being closed during the on-time period.For example, the method is implemented according to at least FIG. 4(a),FIG. 4(b), FIG. 4(d), FIG. 5(a), FIG. 5(b), FIG. 5(c), FIG. 7(a), FIG.7(b), FIG. 7(c), FIG. 8(a), FIG. 8(b), and/or FIG. 9.

According to yet another embodiment, a method for regulating a powerconversion system includes: providing a compensation signal by a firstcontroller terminal based on at least information associated with afirst current flowing through a primary winding of a power conversionsystem; generating a first signal based on at least informationassociated with the compensation signal; and processing informationassociated with the first signal. The method further includes: adjustinga ramping slope associated with a ramping signal based on at leastinformation associated with the first signal; receiving the rampingsignal; generating a drive signal based on at least informationassociated with the ramping signal; and outputting the drive signal froma second controller terminal to a switch to affect the first current.For example, the method is implemented according to at least FIG. 4(a),FIG. 4(b), FIG. 5(a), FIG. 5(b), FIG. 6(a), FIG. 6(b), FIG. 7(a), FIG.7(b), FIG. 8(a), FIG. 8(c), and/or FIG. 9.

In one embodiment, a system controller for regulating a power conversionsystem includes: a signal generator configured to receive a convertedsignal and a first compensation signal and generate a secondcompensation signal based at least in part on the converted signal andthe first compensation signal, the converted signal being associatedwith an input signal for a power conversion system, the firstcompensation signal being associated with a sensing signal related to afirst current flowing through a primary winding of the power conversionsystem; a modulation component configured to receive the secondcompensation signal and a ramping signal and generate a modulationsignal based at least in part on the second compensation signal and theramping signal; and a drive component configured to receive themodulation signal and output a drive signal based at least in part onthe modulation signal to a switch to affect the first current, the drivesignal being associated with an on-time period, the switch being closedduring the on-time period. The system controller is configured to adjusta duration of the on-time period based at least in part on the convertedsignal and the second compensation signal. For example, the systemcontroller is implemented according to at least FIG. 4(a), FIG. 5(a),FIG. 7(a), FIG. 10(a), FIG. 10(b), FIG. 10(c), FIG. 11(a), FIG. 11(b),FIG. 12(a), and/or FIG. 12(b).

In another embodiment, a method for regulating a power conversion systemincludes: receiving a converted signal and a first compensation signal,the converted signal being associated with an input signal for a powerconversion system, the first compensation signal being associated with asensing signal related to a first current flowing through a primarywinding of the power conversion system; generating a second compensationsignal based at least in part on the converted signal and the firstcompensation signal; receiving the second compensation signal and aramping signal; generating a modulation signal based at least in part onthe second compensation signal and the ramping signal; receiving themodulation signal; and outputting a drive signal based at least in parton the modulation signal to affect the first current, the drive signalbeing associated with an on-time period. The outputting a drive signalbased at least in part on the modulation signal to affect the firstcurrent includes adjusting a duration of the on-time period based atleast in part on the converted signal and the second compensationsignal. For example, the method is implemented according to at leastFIG. 4(a), FIG. 5(a), FIG. 7(a), FIG. 10(a), FIG. 10(b), FIG. 10(c),FIG. 11(a), FIG. 11(b), FIG. 12(a), and/or FIG. 12(b).

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1. A system controller for regulating a power conversion system, thesystem controller comprising: a signal generator configured to receive aconverted signal and a first compensation signal and generate a secondcompensation signal based at least in part on the converted signal andthe first compensation signal, the converted signal being associatedwith an input signal for a power conversion system, the firstcompensation signal being associated with a sensing signal related to afirst current flowing through a primary winding of the power conversionsystem; a modulation component configured to receive the secondcompensation signal and a ramping signal and generate a modulationsignal based at least in part on the second compensation signal and theramping signal; and a drive component configured to receive themodulation signal and output a drive signal based at least in part onthe modulation signal to a switch to affect the first current, the drivesignal being associated with an on-time period, the switch being closedduring the on-time period; wherein the system controller is configuredto adjust a duration of the on-time period based at least in part on theconverted signal and the second compensation signal. 2.-29. (canceled)30. A method for regulating a power conversion system, the methodcomprising: receiving a converted signal and a first compensationsignal, the converted signal being associated with an input signal for apower conversion system, the first compensation signal being associatedwith a sensing signal related to a first current flowing through aprimary winding of the power conversion system; generating a secondcompensation signal based at least in part on the converted signal andthe first compensation signal; receiving the second compensation signaland a ramping signal; generating a modulation signal based at least inpart on the second compensation signal and the ramping signal; receivingthe modulation signal; and outputting a drive signal based at least inpart on the modulation signal to affect the first current, the drivesignal being associated with an on-time period; wherein the outputting adrive signal based at least in part on the modulation signal to affectthe first current includes adjusting a duration of the on-time periodbased at least in part on the converted signal and the secondcompensation signal.